Meaning of Hero's formula

He'ro's for'mula

Pronunciation: (hēr'ōz), [key]
— Geom. Geom.
  1. the formula for the area of a triangle when the sides are given: for a triangle with sides a, b, and c, the area is equal to &Herosform;, where s is equal to one half the perimeter of the triangle.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.