A set of documentation tools: man, apropos and whatis.

The man package includes three tools for finding information and/or documentation about your Linux system: man, apropos, and whatis. The man system formats and displays on-line manual pages about commands or functions on your system. Apropos searches the whatis database (containing short descriptions of system commands) for a string. Whatis searches its own database for a complete word.

The man package should be installed on your system because it is the primary way to find documentation on a Linux system.