what is "whatis"

Ever wondered whether there is a quick tool in Linux / UNIX to tell what other commands are for?

enter whatis

just go to shell and use whatis with whatever command you think of
ex:
whatis ls
ls (1) — list directory contents

whatis w
w (1) — Show who is logged on and what they are doing

whatis whatis
whatis (1) — search the whatis database for complete words