[angersock]

It's like a Y combinator, but straighter?

EDIT: Because, you see, if you straighten out the arms of the Y, it turns into a T. Nevermind. It was a dumb joke.

The serious answer is because it's a Trans-friendly YCombinator. I think.

[veyron]

I figured that T stood for trans, but I subconsciously hoped that it was a real thing ...