A power bulge is a raised part (a bulge) of the hood

Hood (vehicle)

The hood or bonnet is the hinged cover over the engine of motor vehicles that allows access to the engine compartment for maintenance and repair. In British terminology, hood refers to a fabric cover over the passenger compartment of the car...

of a car. The reason for a power bulge is to fit for instance a large engine or air filters that otherwise would not fit. Sometimes a power bulge is used to be able to fit a larger engine into a car that originally was not designed for it or it may be a design choice to be able to get a lower profile. As a power bulge is associated with performance cars it may also be used as a design element to give the impression of a fast car.