Glossary of Terms

The process of spreading loan repayments over time through a fixed schedule of payments. Each payment covers accrued interest first, with the remainder reducing the principal balance. An amortization schedule shows the breakdown of every payment. See the Mortgage Calculator.

The yearly cost of borrowing money, expressed as a percentage of the loan amount. APR includes the interest rate plus fees, making it a more comprehensive measure of loan cost than the interest rate alone. Differs from APY, which compounds interest.

The effective annual return on savings or investments, accounting for compounding within the year. APY is always greater than or equal to the stated interest rate. See the Compound Interest Calculator.

Interest calculated on both the initial principal and the accumulated interest from previous periods. Formula: A = P(1 + r/n)^(nt). Compounding frequency (daily, monthly, annually) significantly affects total returns over long periods.

The difference between the present value of future cash inflows and the cost of an investment, discounted at a given rate. A positive NPV indicates a profitable investment. Used in capital budgeting and project evaluation.

The mean annual growth rate of an investment over a specified period longer than one year. Formula: CAGR = (Ending Value / Beginning Value)^(1/Years) − 1. Commonly used to compare investment performance across different time periods.

A screening measure of body fat based on height and weight. Formula: BMI = weight(kg) / height(m)². WHO classification: Underweight (<18.5), Normal (18.5–24.9), Overweight (25–29.9), Obese (≥30). BMI does not directly measure body fat and may be inaccurate for athletes and older adults. See the BMI Calculator.

The total number of calories you burn in a day, including your basal metabolic rate (BMR) plus energy used for activity. Estimated using the Mifflin–St Jeor equation multiplied by an activity factor. TDEE is the calorie level at which your weight remains stable. See the TDEE Calculator.

The number of calories your body burns at complete rest — the minimum energy required to sustain vital functions like breathing, circulation, and cell production. BMR is the foundation of TDEE calculations. The Mifflin–St Jeor equation is the most accurate clinical estimate for most adults.

The three primary categories of nutrients that provide energy: protein (4 kcal/g), carbohydrates (4 kcal/g), and fat (9 kcal/g). A "macro split" (e.g., 40/30/30 carbs/protein/fat) describes the percentage of total calories from each source. See the Macro Calculator.

A clinically validated formula for estimating resting metabolic rate (RMR), published in 1990 in the Journal of the American Dietetic Association and recommended by the Academy of Nutrition and Dietetics. Males: RMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5. Females: RMR = (10 × kg) + (6.25 × cm) − (5 × age) − 161.

A binary-to-text encoding scheme that represents binary data using 64 printable ASCII characters (A–Z, a–z, 0–9, +, /). Defined in RFC 4648. Commonly used to embed binary data (images, files) in JSON, HTML, or email. Increases data size by approximately 33%. See the Base64 Encoder.

A 128-bit identifier used to uniquely label information in computer systems. Version 4 UUIDs (the most common) are randomly generated. Format: xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx. Defined in RFC 4122. Probability of collision is negligibly small for practical purposes. See the UUID Generator.

A sequence of characters that defines a search pattern, used for string matching, validation, and text manipulation. ECMAScript regex (used in JavaScript) supports character classes, quantifiers, groups, lookaheads, and named captures. See the Regex Tester.

A lightweight, human-readable data interchange format. Uses key-value pairs ({}) and ordered lists ([]). Valid JSON must have quoted string keys, and does not support comments or trailing commas. Defined in RFC 8259. See the JSON Formatter.

A compact, URL-safe token format for transmitting claims between parties. Consists of three Base64URL-encoded parts: header (algorithm), payload (claims), and signature. Defined in RFC 7519. The signature verifies the token hasn't been tampered with — it does not encrypt the payload. See the JWT Decoder.

A method for encoding characters in a URI that are not allowed in the standard ASCII character set. Non-safe characters are replaced with a % followed by two hexadecimal digits (e.g., space → %20). Defined in RFC 3986. See the URL Encoder.

A fixed-size output produced by a hash function from an input of any size. Cryptographic hashes (SHA-256, SHA-512) are deterministic, one-way functions — the same input always produces the same hash, but the hash cannot be reversed to recover the input. See the Hash Generator.

The internet's phonebook — translates human-readable domain names (example.com) into IP addresses. DNS record types include A (IPv4 address), AAAA (IPv6), MX (mail server), CNAME (alias), TXT (verification/SPF), and NS (name server). See the DNS Lookup.

Three-digit codes returned by web servers to indicate the result of an HTTP request. Key ranges: 2xx (success: 200 OK, 201 Created), 3xx (redirects: 301 Moved Permanently, 302 Found), 4xx (client errors: 400 Bad Request, 403 Forbidden, 404 Not Found), 5xx (server errors: 500 Internal Server Error). See the HTTP Status Codes reference.

A subnet mask defines the network portion of an IP address. CIDR notation (Classless Inter-Domain Routing) expresses subnets as a prefix length (e.g., 192.168.1.0/24 means the first 24 bits are the network). /24 = 256 addresses (254 usable). See the Subnet Calculator.

Query string parameters appended to URLs to track the source of web traffic in analytics platforms. Standard parameters: utm_source (traffic origin), utm_medium (channel: email, social, cpc), utm_campaign (campaign name), utm_term (keyword), utm_content (variant). See the UTM Builder.

The number of seconds (or milliseconds in JavaScript) that have elapsed since 00:00:00 UTC on 1 January 1970 — the "Unix epoch." Widely used in databases, APIs, and log files. The 32-bit Unix timestamp overflows on 19 January 2038 (the "Year 2038 problem"). See the Unix Timestamp Converter.

The primary time standard by which the world regulates clocks and time. All time zones are expressed as offsets from UTC (e.g., UTC+5:30 for India, UTC−5 for Eastern Standard Time). UTC is not affected by daylight saving time. It is the successor to GMT.

An international standard for representing dates and times. Format: YYYY-MM-DD for dates, YYYY-MM-DDTHH:mm:ssZ for date-times (Z = UTC). ISO 8601 dates sort correctly in both lexicographic and chronological order, making them ideal for database storage and APIs.