The power plant is the combination of the engine and the propeller which are designed to work together to produce thrust as well as to drive various systems that support the airplane.
Most small aircraft are designed with reciprocating engines. The name reciprocating engine is derived from the back and forth (reciprocating) movement of the pistons.
Common means of classifying reciprocating engines are by cylinder arrangement with respect to the crankshaft. Radial, in-line, v-type or opposed. The method of cooling is liquid or air.
Cessna 172 Skyhawk and the Cessna 162 Skycatcher are horizontally opposed cylinders that are air cooled.