I'm not sure of the usefulness of this expression. Would you provide some context? The only time I've heard it used is in snow skiing wherein the skiier launches himself in the air and spins around completely and continues in the same direction after landing on the snow. On the other hand, to do a 180, or to take suddenly an unexpected opposite action, is commonly used and very useful.

It can mean to turn around and face the same direction you were facing before you turned around. To turn 360 degrees. or To change your mind, which is actually incorrect usage.(This should not be use to describe somebody has changed their mind) To do a 180 means change your mind and is the correct usage for this.

To spin (I'm assuming clockwise) 360 degrees. (A full circle)