Short block is an automotive term describing an engine

Engine

An engine or motor is a machine designed to convert energy into useful mechanical motion. Heat engines, including internal combustion engines and external combustion engines burn a fuel to create heat which is then used to create motion...

 sub-assembly.

A short block is the portion of the engine block below the head gasket

Head gasket

A head gasket is a gasket that sits between the engine block and cylinder head in an internal combustion engine. Its purpose is to seal the cylinders to ensure maximum compression and avoid leakage of coolant or engine oil into the cylinders; as such, it is the most critical sealing application in...

 but above the oil pan. An in-block cam engine will also include the camshaft

Camshaft

A camshaft is a shaft to which a cam is fastened or of which a cam forms an integral part.-History:An early cam was built into Hellenistic water-driven automata from the 3rd century BC. The camshaft was later described in Iraq by Al-Jazari in 1206. He employed it as part of his automata,...

 and timing gear. The overhead cam style of engine will not include the aforementioned parts on the shortblock. A shortblock is usually purchased to upgrade the water jacket

Water jacket

A water jacket is a water-filled void surrounding a device, typically a metal sheath having intake and outlet vents to allow water to be pumped through the void. The flow of water to an external heating or cooling device allows precise temperature control of the device.-Applications:Water jackets...

, piston

Piston

A piston is a component of reciprocating engines, reciprocating pumps, gas compressors and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from...

 size or bore. Assemblies typically include the crankshaft

Crankshaft

The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation...

 installed and balanced along with the main bearing

Main bearing

In a piston engine, the main bearings are the bearings on which the crankshaft rotates, usually plain or journal bearings.All engines have a minimum of two main bearings, one at each end of the crankshaft, and they may have as many as one more than the number of crank pins...

.

A short block is considered destroyed when it either warps or cracks.