The function of a second ring is that it is a

prevents engine oil from going into the combustion chamber and returns excess lubricating oil off the cylinder wall through the return holes in the piston to the oil pan

The function of oil control rings is that it prevents engine oil from going into the combustion chamber and returns excess lubricating oil off the cylinder wall through the return holes in the piston to the oil pan.

cast iron

Piston rings are commonly made from cast iron. Cast iron retains the integrity of its original shape under heat, load, and other dynamic forces. Piston rings seal the combustion chamber, conduct heat from the piston to the cylinder wall, and return oil to the crankcase.

piston skirt

The lower cylindrical portion of the piston which improves piston cooling performance is called piston skirt.

valve recess

The crescent shaped cavity on the piston head top surface is called as valve recess.