environment variable
A named value stored at the operating system level and accessible to processes at runtime, commonly used to configure application behaviour without modifying code.
Full Definition
Environment variables allow developers and operators to inject configuration—such as database URLs, API keys, and feature flags—into applications at runtime without hardcoding values in source code. They are conventionally named in UPPER_SNAKE_CASE (e.g., DATABASE_URL, NODE_ENV). Editors should ensure that environment variable names are formatted in monospace code font and in uppercase. The abbreviated form 'env var' is acceptable in informal documentation; 'envvar' (one word) is sometimes seen in Python ecosystem docs. Do not confuse 'environment variable' with 'configuration file', which stores similar data but in a file rather than the OS environment.
Usage
Usage note: Render environment variable names in monospace code font and UPPER_SNAKE_CASE. 'Env var' is acceptable shorthand in informal contexts.
In Context
- "Set the DATABASE_URL environment variable before starting the server." — Installation guide
- "Never commit API keys to version control; use environment variables instead." — Security best practices guide