A Birdman is the name given to a skydiver using a special jumpsuit, called a wing suit, The wing suit creates an airfoil shape which has fabric sewn between the legs and under the arms. It's also commonly known as a birdman suit.
A wing suit can also be used in BASE jumping by extremely experienced base jumpers.
A Birdman wears parachute equipment which is some times modified for wing suit flying to improve safety. The wing suit flier will deploy the parachute at a planned altitude and unzip the arm wings, so they can reach up to the control toggles for a normal parachute landing.