2.3.2 Displaying a One-line Summary with whatis

If you want just a one-line summary of the command's function, use the whatis command, as shown here:

$ whatis date
date (1)           -display or set the date
$

Notice the number in parentheses after the command name in the above example. This number indicates the section to which this command belongs. Commands are grouped into various categories according to function. Most user commands are in section 1. By common convention, the section number is displayed in parentheses after the name of the command. If you look for the printed manual reference page for a command, you will find it in alphabetical order within its group.