ROM = Read only memory.
A rom is a back up of a catridge video game (like nintendo, super nintendo, etc). They are electronic data, so they don't really look like anything except digital information. We can't tell you where to get them because they are not legal to have unless you own the game and make your own backup. You should be able to google up an answer though by searching for the name of the system you need roms for and the word rom.
Good luck, and remember there is no post links to roms in the forum.