Final answer:
Three quarter coverage helmets are known as open-face helmets, which protect the head but leave the face exposed, differing from full-face, half, and modular helmets.
Step-by-step explanation:
The three quarter coverage helmets are commonly referred to as open-face helmets. These types of helmets cover the back and sides of the head but do not have a face shield, leaving the face exposed. This is contrasted with full-face helmets, which cover the entire head and face, and half helmets, which only cover the top of the head and the area from the forehead to the brows. Lastly, modular helmets are a hybrid between full-face and open-face helmets, featuring a chin bar that can be flipped up.