MTA can refer to a few different things. It most commonly stands for the Metropolitan Transportation Authority, a public authority that operates mass transit in the New York City metropolitan area, including buses, subways, and commuter rails like the Long Island Rail Road and Metro-North Railroad. However, MTA can also stand for Mail Transfer Agent, a software application that transfers electronic mail messages from one computer to another, a crucial component of the email system. Depending on the context, MTA can have very different meanings.