Means Yahoo Answers when referring to the website. Used by mainly Yahoo fans. The expression is from Yahoos logo. The "Y" means Yahoo, The exclamation mark is from the yahoo logo "!" after "Yahoo!" and the "A" is from the Answers part of the logo on the Yahoo Answers webpage.
Johnny: What's that new Viral video about man?
Ryan: Dunno haven't seen it ask on Y!A
The best website on the internet. Just don't say anything about sex, drugs, swear words, masturbation, whores, killing, abuse, violence, Alabama Hot Pockets, or anything else FUN. If you do, beware... you will get reported and will get a violation. And not the good kind.
Person 1) Someone on Y!A said I should break up with you.
Person 2) Maybe I should break your face ho!