A T-Spin is an epic spin(not a simple flip, though) sometimes done by SimpleFlips while playing Tetris.
T-Spins are rotations of the T-Tetromino(hence the name), while spinning the tetromino into a tight gap that's normally not possible by normal physics, Thankfully due to how rotating(which are instant rotation-teleports of 90 degrees without any startup) works in Tetris, it abides by the laws of physics. Some people have deduced that maybe the T stands for TJ "Henry" Yoshi, Tingle, sillicone Toys, Tape, and TUP, but all of these except TUP except maybe not are false. It always refers to the shape, the taste, and the texture.
Despite the apparent lack of humor in T-Spins, T-Spins are, considered a joke, for it is a relevant enough move in SimpleFlips arsenal that they have obtained an BUP-themed emote (named SimTUP) and are often the source of many combos big enough to boost the legend himself to the very top of the leaderboard.