A formula giving the area of a triangle in terms of the lengths of its sides.
For a triangle with sides of length a, b, and c, the area A = √s(s − a)(s − b)(s − c), where s = ½(a + b + c).
Late 19th century. From the genitive of the name of Hero (also Heron) of Alexandria (fl. ca.d. 60), scientist and engineer, who described the formula.