whatis —
describe what a command is
  
    | whatis | [ -Cpath]
      command ... | 
The whatis program queries the apropos database built by
  makemandb(8). It searches for
  manual pages with name command and outputs name of the
  matching manual pages along with the section and the brief description from
  the NAME section.
It supports the following options:
  - -Cpath
- Use different man(1)
      configuration file than the default,
      /etc/man.conf.
  - /etc/man.conf
- The location of the Sqlite FTS database can be configured using the
      _mandbtag.
Thewhatis command appeared in 3.0BSD. It was rewritten
  in NetBSD 6.0 to use the SQLite index created by
  makemandb(8).