A short block engine is an assembly piece used in manufacturing a complete and functioning engine. The short block is the part that goes above the oil pan and below the head gasket.
Although not complete, short block engines usually come with pistons that connect rods to cranks. An oil pump, gaskets and cylinder pumps are additional parts needed with a short block engine. Mechanics often use short block engines as a quicker way to rebuild engines that are in need of repair. Short block engines are different from long block engines, which require less time and parts in the installation process.