An '.env' file is a plain text file that stores environment variables. These variables are key-value pairs that define the configuration settings for an application or system. They are commonly used to separate configuration from code, making it easier to manage different environments (e.g., development, testing, production) without modifying the application's source code. This separation enhances security by preventing sensitive information, such as API keys, database passwords, and other credentials, from being hardcoded directly into the application. Instead, these values are stored in the '.env' file and loaded into the application's environment at runtime. This approach also simplifies deployment and maintenance, as configuration changes can be made by simply modifying the '.env' file without requiring code recompilation or redeployment. The file is typically located in the root directory of the project and is often excluded from version control systems to prevent accidental exposure of sensitive data. Libraries and frameworks in various programming languages provide mechanisms to easily load and access environment variables from '.env' files.