[IndySam]

Originally Posted by GeeTwo

The piston is the piece inside the cylinder which is pushed by the air and which in turn pushes and pulls the output shaft relative to the main cylinder body. P⁴s (pernickety persons' pet peeves) aside, the term piston is commonly used for the whole thing because it won't be confused with the shape of a pneumatic tank, compressor, motor, wheel, or shaft.

OBTW, if the one in the render above is a cylinder, we can also include any sort of extrusion as a cylinder by shape.

I don't know a single person in industry who would call it a piston. As mentors it's up to us to teach proper terminology.