It's the fourth Shin Megami Tensei game.
Persona doesn't have the SMT name in Japan, it's a sub-series and Atlus gives all them the SMT name when localizing them.
Games with the SMT name are:
Shin Megami Tensei, SMT II, SMT if..., SMT III: Nocturne, SMT Strange Journey, SMT IV
The MMO too, SMT Imagine
Everything else is given the SMT name during localization, so mainly these series:
Persona, Digital Devil Saga, Devil Summoner, Devil Survivor
All of the games tend to share themes or gameplay ideas, and all of them have the mythological demons and deities that you fight against and/or fight alongside of. I think Atlus adds the SMT name on for brand recognition, but I think they are usually close enough for it to make sense.
Besides, it can be confusing even without the added name, the numbered games plus Strange Journey and Imagine are part of the main series while SMT if... was a "what if" story that led to the creation of the Persona series, which I believe also has some ties with the Devil Summoner games.
All the games are usually independent of others, even within their own series, so you don't need to be worried about being lost when starting a game.