Datum

[Sarah]

The quantities or relations which are assumed to be given inany problem. Datum line (Surv.), the horizontal or base line, fromwhich the heights of points are reckoned or measured, as in the planof a railway, etc.

[Sarah]

-noun

1. a person of male gender who is considered by his piers to be a stud
2. a person of male gender who has a frequency to become erect while listening to classical music

[Sarah]

The singular of data; but this form is never used anymore.
One example that shows Gresham's law, which says bad