AO is "Adults Only", the ESRB's strictest rating. See, the M (for Mature, meaning 17 and up) version of LSL has breasts, S&M, strap-on dildos, bukkake, lesbian and gay sex, hermaphrodites, hooking, stripping, voyeurism, and masturbating monkeys, while the AO version has, well, more, I guess. Probably you get to see a vagina. But you have to be 18 to play this one. You can only play the other one if you're still 17. It's only offered online, since stores don't sell games rated AO, since apparently they're not aware of how non-sensical the whole thing is.

Leisure Suit Larry: Magna Cum Laude Uncut and Uncensored [VUGames]