1 n-count If you make a U-turn when you are driving or cycling, you turn in a half circle in one movement, so that you are then going in the opposite direction.
2 n-count If you describe a change in a politician's policy, plans, or actions as a U-turn, you mean that it is a complete change and that they made the change because they were weak or were wrong., (disapproval)
...a humiliating U-turn by the Prime Minister.