apropos command in Linux is basically useful for those who remember not any exact command but a few keywords related to the command which defines its functions. So, with the usage of apropos, the users can search the Linux man page with the provided keyword to find the right command and its functions.

Here comes the syntax the use apropos command in Linux

apropos [OPTION…] Keyword
According to Linux man page, the apropos command is described as:

Each manual page has a short description available within it. apropos
searches the descriptions for instances of keyword.

keyword is usually a regular expression, as if (-r) was used, or may
contain wildcards (-w), or match the exact keyword (-e). Using these
options, it may be necessary to quote the keyword or escape () the
special characters to stop the shell from interpreting them.

The standard matching rules allow matches to be made against the page
name and word boundaries in the description.

The database searched by apropos is updated by the mandb program.
Depending on your installation, this may be run by a periodic cron job,
or may need to be run manually after new manual pages have been
installed.