The Geek Stuff posted a tutorial that will explain the three W commands. The three Ws are whatis, whereis and which commands.

Whatis command is helpful to get brief information about Linux commands or functions. Whatis command displays man page single line description for command that matches string passed as a command line argument to whatis command. Whatis command searches for string in its index databases which is maintained by mandb program. Whatis command picks short description of NAME section of man page of command that matches to input given to the whatis command.

Whatis provides several command line options to help user in getting brief information of specific Linux commands as per their need or interest.

  12 Linux Which Command, Whatis Command, Whereis Command Examples