A
cylinder block is an structure the
cylinder(s) of a
reciprocating engine and often some or all of their associated surrounding structures (
coolant passages, intake and exhaust passages and ports, and
crankcase). The term
engine block is
often used synonymously with "cylinder block" (although technically distinctions can be made between
en bloc cylinders as a discrete unit versus engine block designs with yet more integration that comprise the crankcase as well).