"The Drop" over on the PS Blog featured a game that was available on both PS3 and the new PS Vita, officially dubbing the buy-one-get-one nature of title as a "Cross Purchase".
Rey Guttierez labeled the game as such, allowing all developers and publishers of future games with this marketing strategy to fall back on one term to better clarify the deal to consumers. It may take a while before everyone uses the term, but its safe to say that as long as the talented team at the PlayStation Blog continue to use it in this context, then all must use it.
Currently, it can be confusing reading about such a thing coming from three different developers. They use a ton of words to convey the same message: buy it on one, get the other for free. This applies to over a handful of released or upcoming PSN titles, as well as various DLC add-ons for games like Hustle Kings and Ultimate Marvel vs Capcom 3.