Hide is a thief skill used to attempt to conceal yourself in a room. Hide may  
be practiced at a guildmaster. As soon as you do anything, you are no longer
hiding.

In order to hide, you must not make any noise, so avoid being in possession
of anything that hums.  Also, you must not emit too much light - in some
situations, ambient light will drown out any light sources you carry, but
to hide in a dark room, you must not have anything that glows.