Multi-region allows you to play DVD's from certain part's of the world - Europe, America etc iirc.
Also just to clear some technical jargon up for you..
CD & DVD-ROMs will only read cd and dvd discs
DVD-RW allows you to write to a disc
and IDE and SATA are the type of connections they use, IDE was used for older computers, that's the thick "ribbon-like" grey cable. And SATA is used in new computers it's a thin cable usually red.