Definition of a Compound

A compound is a substance formed when two or more elements are chemically combined together. It is represented by a formula.

E.g. when hydrogen and oxygen are combined in 2:1 ratio respectively, water is a compound formed.

$\mathrm{H}2\left(\mathrm{g}\right)+\frac{1}{2}{\mathrm{O}}_2\left(\mathrm{g}\right)\to {\mathrm{H}}_{2}0\left(\mathrm{l}\right)$