MPEG Transport Stream (or MPEG-2 Transport Stream) is an MPEG multimedia format that allows interleaving more than one Packetized Elementary Stream in a single file. It is an alternative to MPEG Program Stream, designed to work better with certain kinds of streaming. It was introduced in the MPEG-2 standard. There is a variant format named M2TS, used with Blu-ray discs.
Alternatively, you got here like I did by selecting a typescript file. That's wrong, that's your browser doing that. There's no official standard for typescript.