During the intake stroke, what direction is the piston moving?

During the intake stroke of an internal combustion engine, the piston moves downward within the cylinder. This downward movement is actually pulling air (and potentially fuel, in the case of a carbureted engine) into the combustion chamber. When considering the locations defined as top dead center (TDC) and bottom dead center (BDC), TDC is the highest point the piston can reach within the cylinder, and BDC is the lowest point.

As the piston moves from TDC during the intake stroke, it creates a vacuum that allows air (or the air-fuel mixture) to enter the cylinder. This is characterized as moving away from TDC toward BDC. Thus, describing the motion of the piston as moving away from top dead center accurately reflects the correct direction during the intake stroke.