Configuration is the process of specifying the settings used for a system or application
Configuration is used to customize the behavior of a program. It is commonly done using static configuration files that can be composed in any common text editor, but some applications provide tools (sometimes even with graphical interfaces) to create, modify, and verify the syntax of their configuration files.
Some programs only read their configuration files at startup. Others periodically check the configuration files for changes. Users can instruct some programs to re-read the configuration files and apply the changes to the current process, or indeed to read arbitrary files as a configuration file.