A set of symbols showing the composition of a chemical compound. A formula lists the elements contained within it and indicates the number of atoms of each element with a subscript numeral if the number is more than 1. For example, H2O is the formula for water, where H2 indicates two atoms of hydrogen and O indicates one atom of oxygen.
A set of symbols expressing a mathematical rule or principle. For example, the formula for the area of a rectangle is a = lw, where a is the area, l the length, and w the width.