The letter Y. As long as you’re illiterate.
The Y turn on beam is surprisingly popular these days despite its seemingly increased risk compared to the equally valued L turn. In the days when a turn was required to be counted for difficulty, the L turn was way more popular, but now they’re about equal. Probably because if you’re bothering to do one of these turns now, that means you’re pretty good at turning and competent with a Y position. Otherwise, you’re just going to do a full turn or wolf it.
Theoretically, the leg is supposed to be held in a split throughout, but more often you’ll see gymnasts touch their leg in split position for exactly one millisecond of the turn and do something halfway between an L and a Y for the rest of it going, “I do Y spin!”