Tappet n. : A lever or projection moved by some other piece, as a cam, or intended to tap or touch something else, with a view to produce change or regulate motion.

Example:
I just bought a comp cam (Hydraulic flat Tappet) do i need to buy new lifters as well?

Taxonomy
tappet, valve, valve stem, free encyclopedia, cylinder head, rocker arm, linear motion, cam lobe, projection, downward force, camshaft, adjustment, exhaust valve, overhead valve engines, arm assembly, search, Unsourced, cam drive.

Defination from the web:
tappet just under the cam lobe. A tappet in mechanical engineering is a projection which imparts a linear motion to some other component within an assembly. ...