Searches through headers of manpages for a string. It is equivalent to man -k.
Apropos is useful when you know what you want to do, but don't know the name of the tool required. For example: "apropos rename" gives lots of results, including this useful one:
Often a wrapper for the man -k command, the apropos command is used to search all manual pages for the string specified. This is often useful if one knows the action that is desired, but does not remember the exact command or page name.
Sample usage
The following example demonstrates the output of the apropos command:
$ apropos mount
free (1) - Display amount of free and used memory in the system
mklost+found (8) - create a lost+found directory on a mounted Linux second extended file system
mount (8) - mount a file system
mountpoint (1) - see if a directory is a mountpoint
ntfsmount (8) - Read/Write userspace NTFS driver.
sleep (1) - delay for a specified amount of time
switch_root (8) - switch to another filesystem as the root of the mount tree.
umount (8) - unmount file systems
In this example, apropos is used to search for the string "mount", and apropos returns the indicated man pages that include the term "mount".