What type of turn is not legal in all places?

If you have a green ARROW to turn left, your turn is protected and oncoming traffic is stopped. If you have an ordinary green LIGHT, your turn is permitted but not protected, and you are expected to yield to oncoming traffic before making your turn.

A U-turn in driving refers to performing a 180° rotation to reverse the direction of travel. It is called a "U-turn" because the maneuver looks like the letter U. In some areas, the maneuver is illegal, while in others, it is treated as a more ordinary turn, ... Laws vary by jurisdiction as to when a U-turn may or may not be legal.