Definition:Unit


 * Numbers: An instance of the number 1|$1$ (one).
 * Abstract Algebra: Unit of Ring.
 * Set Systems: Unit of System of Sets.
 * Algebras: Unit of a unitary algebra.

The concepts are related: it is apparent that the unit of an algebra of sets $\mathcal S$ is the unity of $\mathcal S$ considered as a ring $\struct {\mathcal S, *, \cap}$.

It may also refer to
 * Unit of Measurement: A definite magnitude of a physical quantity which is agreed by convention.

Also see

 * Definition:Unity