in the terms of this site, a ROM is a dump of a game (i.e. SNES ROM), an ISO is a disc image (use Alcohol 120% to make an ISO), and BIOS is what makes a console work (cant run a lot of emulators without a BIOS). they're illegal to distribute due to copyright laws.
and just because you dont know what they stand for doesnt mean you cant stop from using that one. that's not a valid excuse "sorry officer, i didnt mean to shoot that guy...i had no idea what a 'gun' did..."