Welcome to Eorzea!

I'm not entirely certain, but I think the person was referring to Astrologian abilities (AST) which is a healer Job that uses card shuffles to make different effects on their spells - the other player was probably talking about one of their abilities (I'm not sure, I've only ever messed around once with AST and still haven't grasped the full mechanics of the Job). So don't worry if you didn't understand, I would have been just as clueless as you are!

For a more general list of the most common player-created terms, acronyms, abbreviations and slang used in the game, this list is a very good guide to deciphering it all. Hopefully this has helped.