Configuration files are text files used by software applications to define settings and preferences. They allow users and developers to customize how a program operates without altering the source code. Common formats for configuration files include JSON, XML, and INI. These files typically contain key-value pairs, where each key represents a specific setting, and the corresponding value defines its state. For example, a configuration file might specify the database connection details or user interface options. By modifying these files, users can easily adjust the behavior of applications to suit their needs.