Illustrated Glossary of Organic Chemistry

Pi bondbond): A bond formed by the overlap of p orbitals on adjacent atoms, perpendicular to any sigma bond(s) between the same atoms. Indicated in a Kekule structure or bond-line structure as an extra line parallel to the line which represents the sigma bond. A pi bond has two orbital lobes, one above and one below the plane of the sigma bond.

Pi Bond of Ethylene

Kekule structure   
Molecular model kit