My understanding is T for text-based [1], the term is used about e.g. DOS programs too where the text interface is not historically called a terminal.

[1]: https://en.wikipedia.org/wiki/Text-based_user_interface

Yes. The term has been around for at least a few decades, but only became somewhat more widely used in the past decade. Only really known by people who spend a lot of time on the command line.

Not to be confused with CLI, which is literally for people who spend a lot of time on the Command Line :)