The machine epsilon gives an upper bound on the relative error due to rounding in floating point arithmetic. The quantity is also called "macheps" or "unit roundoff".
The IEEE standard does not define the terms machine epsilon and unit roundoff, so differing definitions of these terms are in use, which can cause some confusion.
The following different definition is much more widespread outside academia: Machine epsilon is defined as the smallest number that, when added to one, yields a result different from one.
