A .props file, commonly referred to as a Java Properties file, is a simple text-based file format primarily used in Java-related applications to store configuration settings, application parameters, and environment variables. The format follows a straightforward key-value pair structure, where each line typically contains a single setting defined by a key, followed by an equals sign or a colon, and then the corresponding value. Because of its simplicity and human-readability, it is widely utilized for managing application behavior without requiring recompilation of the source code. While it originated in the Java ecosystem, the format is now frequently used across various programming languages and frameworks for lightweight configuration management. It supports comments using the '#' or '!' characters, allowing developers to document settings directly within the file. Despite its popularity, it lacks support for complex hierarchical data structures, which often leads developers to migrate to formats like JSON, YAML, or TOML for more intricate configuration needs.