That's not an acronym. P.T. was actually a game. Developed by Kojima Productions (Under the direction of Hideo Kojima himself) and published by Komani, PT was a first person horror game released on the PS4 as a kind of promo or demo for an unnamed, upcoming horror game, eventfully confirmed as a new Silent Hill game called Silent Hills. However, that game was cancelled, relationships between Kojima and Komani deteriorated (as I'm sure you're aware) and the ever spiteful publisher removed PT from the PlayStation store, eventually removing a re-download option for those who had actually bought it, because FucKonami. A damn shame that was too as PT was very well received.