Definition:Ordinal/Also known as

Ordinal: Also known as
An ordinal is also known as an ordinal number.

For a given well-ordered set $\struct {X, \preceq}$, the expression:
 * $\map {\mathrm {Ord} } X$

can be used to denote the unique ordinal which is order isomorphic to $\struct {X, \preceq}$.