Glossary

Definitions of technical, financial, health, and SEO terms used across sadiqbd tools.

Developer & Technical

API (Application Programming Interface): A set of rules and protocols that allows different software applications to communicate with each other. In web development, REST APIs use HTTP methods (GET, POST, PUT, DELETE) to exchange JSON data between client and server. Used by the REST API Checker.
Base64: A binary-to-text encoding scheme that converts binary data into a string of printable ASCII characters using 64-character alphabet (A–Z, a–z, 0–9, +, /). Commonly used to embed images in HTML/CSS, encode email attachments, and transmit data safely in URLs. Defined in RFC 4648. See Base64 Encoder & Decoder.
Bcrypt: A password hashing function designed to be computationally expensive to slow down brute-force attacks. Uses a configurable cost factor (work factor) so hashing remains slow as hardware improves. Recommended by NIST SP 800-63B for password storage. See Bcrypt Generator.
Color Models (RGB, HSL, HEX): Systems for representing colours digitally. RGB (Red, Green, Blue) uses three 0–255 values. HEX is the hexadecimal shorthand (e.g. #FF5733). HSL (Hue, Saturation, Lightness) is more intuitive for adjusting colours. All three are interconvertible and standardised in W3C CSS Color Level 4. See Color Converter.
Cron Expression: A syntax used to schedule automated tasks at specified times or intervals on Unix systems. Five fields: minute, hour, day of month, month, day of week. Example: 0 9 * * 1 means "9am every Monday". See Cron Expression Explainer.
Hash Function (MD5, SHA-256, SHA-512): A function that transforms input data of any size into a fixed-size output (digest). Cryptographic hashes are one-way — you cannot reverse the output to recover the input. Used for file integrity verification, password storage, and digital signatures. MD5 defined in RFC 1321; SHA-2 in NIST FIPS 180-4. See Hash Generator.
HTML Entities: Special codes used in HTML to represent characters that have special meaning in HTML markup (such as <, >, &) or characters outside ASCII. For example, & renders as &. Defined in the WHATWG HTML Living Standard. See HTML Entities Encoder.
JSON (JavaScript Object Notation): A lightweight, human-readable data interchange format based on a subset of JavaScript syntax. Uses key-value pairs and arrays to structure data. Defined in RFC 8259 and ECMA-404. Widely used in REST APIs and configuration files. See JSON Formatter.
JWT (JSON Web Token): A compact, URL-safe token format for securely transmitting information as a signed JSON object. A JWT has three parts separated by dots: header (algorithm), payload (claims), and signature. Defined in RFC 7519. Commonly used for authentication in web APIs. See JWT Decoder.
Password Entropy: A measure of a password's unpredictability, expressed in bits. Higher entropy means a stronger password, harder to guess by brute force. Calculated from character set size and password length. NIST SP 800-63B recommends prioritising length over mandatory complexity rules. See Password Generator.
Regex (Regular Expression): A sequence of characters that defines a search pattern for matching, finding, or replacing strings. Example: ^\d{3}-\d{4}$ matches a 7-digit phone number. PHP uses PCRE2 (Perl-Compatible Regular Expressions). See Regex Tester.
REST API: An architectural style for web services using standard HTTP methods (GET, POST, PUT, DELETE, PATCH) and stateless communication. Resources are identified by URLs; data is typically exchanged as JSON. HTTP semantics defined in RFC 9110. See REST API Checker.
Unix Timestamp: The number of seconds elapsed since January 1, 1970, 00:00:00 UTC (the Unix epoch), not counting leap seconds. Used universally in programming to represent points in time as a single integer. Defined in POSIX; referenced in RFC 3339. See Unix Timestamp Converter.
URL Encoding (Percent Encoding): A mechanism to encode special characters in URLs using % followed by two hexadecimal digits (e.g. space → %20, & → %26). Necessary because URLs can only safely contain a limited set of ASCII characters. Defined in RFC 3986. See URL Encoder & Decoder.
UUID (Universally Unique Identifier): A 128-bit identifier formatted as 8-4-4-4-12 hexadecimal groups (e.g. 550e8400-e29b-41d4-a716-446655440000). Designed to be globally unique without a central authority. Version 4 (random) is most common. Defined in RFC 9562. See UUID Generator.

SEO

Alt Text: A text description of an image in the HTML alt attribute. Used by screen readers for accessibility, displayed when images fail to load, and indexed by search engines. Required for WCAG 2.1 Success Criterion 1.1.1. See Image Alt Checker.
Canonical URL: The preferred URL when multiple URLs serve the same or similar content. Specified with <link rel="canonical" href="..."> in the HTML head. Prevents duplicate content penalties and concentrates link equity on the preferred URL. Defined in RFC 6596. See Canonical Tag Generator.
Hreflang: An HTML attribute specifying the language and geographic region of a page, helping search engines serve the correct regional version. Format: <link rel="alternate" hreflang="en-US" href="...">. Uses BCP 47 language tags. See Hreflang Generator.
Meta Description: An HTML meta tag providing a brief summary (150–160 characters) of a page. Often displayed as the snippet text in search results. While not a direct ranking factor, a compelling meta description improves click-through rates. Defined in the WHATWG HTML Living Standard. See Meta Tag Generator.
Open Graph Protocol: A protocol enabling web pages to become rich objects when shared on social platforms (Facebook, LinkedIn, etc.). Uses <meta property="og:..."> tags to define title, description, image, and URL for social previews. Published at ogp.me. See Open Graph Generator.
HTTP Redirects (301/302/307/308): Server responses that send browsers to a different URL. 301 (Moved Permanently) passes link equity; 302 (Found) is temporary; 307 (Temporary Redirect) preserves the HTTP method; 308 (Permanent Redirect) preserves method permanently. Defined in RFC 9110 §15. See Redirect Mapper.
Robots.txt: A text file at the root of a website (e.g. /robots.txt) that instructs web crawlers which pages or sections to crawl or avoid. Uses User-agent directives to target specific bots. Formalised in RFC 9309. See Robots.txt Generator.
Schema Markup (Structured Data): Code added to web pages to help search engines understand content. Uses vocabulary from Schema.org and formats like JSON-LD. Enables rich results in Google Search (FAQ dropdowns, star ratings, breadcrumbs). See Schema Generator.
SERP (Search Engine Results Page): The page displayed by a search engine in response to a query. Contains organic results, paid ads, featured snippets, knowledge panels, and other SERP features. Structured data and page quality determine which SERP features a page qualifies for. See SERP Preview.
XML Sitemap: A file listing all important URLs on a website, helping search engines discover and index pages efficiently. Follows the Sitemaps.org protocol. Can include <lastmod>, <changefreq>, and <priority> for each URL. See XML Sitemap Generator.
UTM Parameters: URL query parameters (utm_source, utm_medium, utm_campaign, utm_term, utm_content) appended to URLs to track traffic sources in analytics tools. Example: ?utm_source=newsletter&utm_medium=email. Originally developed for Urchin, now used with Google Analytics. See UTM Builder.

Financial

Amortization: The process of paying off a loan through regular scheduled payments over time. Each payment covers interest (charged on the outstanding balance) and principal (reducing the loan balance). An amortization schedule shows how each payment splits between interest and principal over the loan's life. See Loan Planner.
Compound Interest: Interest calculated on both the initial principal and the accumulated interest from previous periods. Formula: A = P(1 + r/n)^(nt), where P is principal, r is annual rate, n is compounding frequency, t is years. More powerful than simple interest over long periods — the foundation of long-term wealth creation. See Compound Interest Calculator.
EMI (Equated Monthly Installment): A fixed monthly payment made by a borrower on a specific date each month, covering both principal and interest. Formula: EMI = [P × r × (1+r)^n] / [(1+r)^n - 1]. Used for home loans, car loans, and personal loans. See EMI Calculator.
Fixed Deposit (FD): A financial instrument offered by banks where a lump sum is deposited for a fixed term at a predetermined interest rate. Interest is typically compounded quarterly. At maturity, the investor receives principal plus accumulated interest. See FD Calculator.
GST (Goods and Services Tax): A value-added tax levied on the supply of goods and services, collected at each stage of the supply chain. In India, GST has slabs of 0%, 5%, 12%, 18%, and 28%. The final consumer bears the full tax burden. See GST & VAT Calculator.
Inflation: The rate at which the general level of prices rises over time, decreasing purchasing power. Measured using the Consumer Price Index (CPI). Central banks typically target 2–3% annual inflation. At 7% annual inflation, purchasing power halves in about 10 years. See Inflation Calculator.
Recurring Deposit (RD): A savings scheme where a fixed amount is deposited monthly for a predetermined period. Banks pay compound interest, typically compounded quarterly. At maturity, the investor receives total deposits plus accumulated interest. See RD Calculator.
Simple Interest: Interest calculated only on the original principal, not on accumulated interest. Formula: I = P × r × t, where P is principal, r is annual rate, and t is time in years. Less common than compound interest for savings accounts. See Simple Interest Calculator.
SIP (Systematic Investment Plan): An investment method where a fixed amount is invested regularly (usually monthly) in mutual funds. Benefits from rupee cost averaging — buying more units when prices are low and fewer when high. Regulated by SEBI in India. See SIP Calculator.
VAT (Value-Added Tax): A consumption tax collected at each stage of production and distribution. Each business charges VAT on its output and claims back VAT paid on its inputs. The final consumer pays the full tax. Standard rates vary by country (e.g. 20% in UK). See GST & VAT Calculator.

Health

BMI (Body Mass Index): A measure of body weight relative to height: weight(kg) / height(m)². WHO classifications: Underweight (<18.5), Normal (18.5–24.9), Overweight (25–29.9), Obese (≥30). A screening tool — does not account for muscle mass or fat distribution. See BMI Calculator.
BMR (Basal Metabolic Rate): The number of calories the body burns at rest to sustain basic life functions (breathing, circulation, cell production). Calculated using the Mifflin-St Jeor equation (1990). BMR is the baseline for calculating total daily calorie needs. See BMR Calculator.
Body Fat Percentage: The proportion of fat mass to total body weight. ACE guidelines: fitness-level ranges are 21–24% for women and 14–17% for men. Measured using DEXA scans, hydrostatic weighing, skinfold calipers, or bioelectrical impedance. See Body Fat Calculator.
Calorie (kcal): The unit of energy in food. One kilocalorie (Calorie with capital C) is the energy needed to raise 1 kg of water by 1°C. Daily calorie needs depend on BMR, activity level, age, and goals. USDA Dietary Guidelines recommend 1,600–3,000 kcal/day depending on individual factors. See Calorie Intake Calculator.
Macronutrients (Macros): The three main nutrient categories that provide energy: carbohydrates (4 kcal/g), proteins (4 kcal/g), and fats (9 kcal/g). IOM Dietary Reference Intakes recommend 45–65% carbs, 10–35% protein, and 20–35% fat of total daily calories. See Macro Calculator.
TDEE (Total Daily Energy Expenditure): The total calories burned per day: BMR × activity multiplier (sedentary ×1.2, lightly active ×1.375, moderately active ×1.55, very active ×1.725). Knowing your TDEE helps determine the calorie target for weight loss, maintenance, or gain. See Calorie Intake Calculator.

Units & Converters

Binary Prefixes (KiB, MiB, GiB): Standardised prefixes for powers of 2, defined in IEC 80000-13. 1 KiB (kibibyte) = 1,024 bytes; 1 MiB (mebibyte) = 1,048,576 bytes; 1 GiB (gibibyte) = 1,073,741,824 bytes. Distinct from SI decimal prefixes: 1 KB = 1,000 bytes; 1 MB = 1,000,000 bytes. See Data Storage Converter.
IANA Time Zone Database: The authoritative database of the world's time zones, maintained by IANA and used by virtually all operating systems and programming languages. Time zones are identified by names like America/New_York or Asia/Dhaka. Updated regularly to reflect daylight saving time changes. See Time Zone Converter.
SI Units (International System of Units): The modern metric system — the world's most widely used measurement system. Defines seven base units: metre (length), kilogram (mass), second (time), ampere (electric current), kelvin (temperature), mole (amount), and candela (luminous intensity). Maintained by NIST and published in ISO 80000 standards. See Length Converter.

Text & Encoding

ASCII (American Standard Code for Information Interchange): A character encoding standard that assigns numeric values (0–127) to 128 characters — uppercase and lowercase letters, digits, punctuation, and control characters. The foundation of modern text encoding. All ASCII characters are valid UTF-8 (UTF-8 is a superset of ASCII). See Number Base Converter.
Lorem Ipsum: Standard placeholder text derived from Cicero's "de Finibus Bonorum et Malorum" (45 BC), deliberately scrambled into nonsense. Used in typesetting and design to preview layouts without distracting readable content. The text begins: "Lorem ipsum dolor sit amet, consectetur adipiscing elit..." See Lorem Ipsum Generator.
Morse Code: An encoding system representing letters and digits as sequences of dots (short signals) and dashes (long signals), originally transmitted electrically or as sound. Standardised by the ITU as International Morse Code (ITU-R M.1677-1). SOS (··· --- ···) is the universal distress signal. See Morse Code Translator.
ROT13: A simple letter substitution cipher that shifts each letter 13 positions in the alphabet (A→N, B→O, etc.). Applying ROT13 twice returns the original text, making it self-inverse. Used informally online to obscure spoilers or punchlines. Not a security measure — purely obfuscation. See ROT13 Encoder.
Unicode: A universal character encoding standard that assigns a unique code point to every character from every writing system — currently over 140,000 characters across 150+ scripts. Unicode text is typically stored as UTF-8, UTF-16, or UTF-32. Maintained by the Unicode Consortium. See Character Frequency Counter.
UTF-8: A variable-width character encoding that represents Unicode code points using 1–4 bytes. ASCII characters are encoded as single bytes (backward compatible with ASCII). The dominant encoding on the web — over 98% of websites use UTF-8. Defined in RFC 3629. See Character Frequency Counter.