A unit in a ring is an element 
such that there exists 
where 
.
Ring Unit
See also
RingExplore with Wolfram|Alpha
References
Atiyah, M. F. and Macdonald, I. G. Introduction to Commutative Algebra. Menlo Park, CA: Addison-Wesley, 1969.Referenced on Wolfram|Alpha
Ring UnitCite this as:
Weisstein, Eric W. "Ring Unit." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/RingUnit.html