A cylinder block is an integrated structure comprising the cylinder(s)

Cylinder (engine)

A cylinder is the central working part of a reciprocating engine or pump, the space in which a piston travels. Multiple cylinders are commonly arranged side by side in a bank, or engine block, which is typically cast from aluminum or cast iron before receiving precision machine work...

 of a reciprocating engine

Reciprocating engine

A reciprocating engine, also often known as a piston engine, is a heat engine that uses one or more reciprocating pistons to convert pressure into a rotating motion. This article describes the common features of all types...

 and often some or all of their associated surrounding structures (coolant

Antifreeze

Antifreeze is a freeze preventive used in internal combustion engines and other heat transfer applications, such as HVAC chillers and solar water heaters....

 passages, intake and exhaust passages and ports, and crankcase

Crankcase

In an internal combustion engine of the reciprocating type, the crankcase is the housing for the crankshaft. The enclosure forms the largest cavity in the engine and is located below the cylinder, which in a multicylinder engine are usually integrated into one or several cylinder blocks...

). The term engine block is often used synonym

Synonym

Synonyms are different words with almost identical or similar meanings. Words that are synonyms are said to be synonymous, and the state of being a synonym is called synonymy. The word comes from Ancient Greek syn and onoma . The words car and automobile are synonyms...

ously with "cylinder block" (although technically distinctions can be made between en bloc

Monobloc engine

A monobloc or en bloc engine is an internal-combustion piston engine where some of the major components: cylinder head, cylinder block, or crankcase are formed, usually by casting, as a single integral unit, rather than being assembled later...

 cylinders as a discrete unit versus engine block designs with yet more integration that comprise the crankcase as well).

In the basic terms of machine element

Machine element

Machine elements are basic mechanical parts used as the building blocks of most machines. Most are standardized to common sizes, but customs are also common for specialized applications.-Types:*Shafts**Couplings*Keys*Splines*Bearings**Roller bearings...

s, the various main parts of an engine (such as cylinder(s), cylinder head(s)

Cylinder head

In an internal combustion engine, the cylinder head sits above the cylinders on top of the cylinder block. It closes in the top of the cylinder, forming the combustion chamber. This joint is sealed by a head gasket...

, coolant passages, intake and exhaust passages, and crankcase) are conceptually distinct, and these concepts can all be instantiated as discrete pieces that are bolted together.