Muscle contraction, one that occurs when a muscle fiber lengthens or shortens

The reverse of thermal expansion

Tensor contraction in tensor theory (in mathematics)

Braille contraction, used to decrease space and increase reading speed

Edge contraction or vertex contraction, graph operations used in graph theory

Contraction mapping, in mathematics, a type of function on a metric space

A structural rule in proof theory, see idempotency of entailment

Economic contraction, a reversal of economic growth; the opposite of economic expansion.

Contraction (childbirth), a contraction during childbirth (basically referring to muscle contraction)

In linguistic morphology, a contraction is a new word formed from two or more individual words. See also abbreviation and acronym.

In phonetics, a contraction or syncope is the loss or reduction of sounds within a word.