double bond

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A covalent bond in which two electron pairs are shared between two atoms.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun chemistry A covalent bond in which two electron pairs (instead of the usual one) are shared between two atoms; most common between carbon atoms and carbon, oxygen or nitrogen atoms, but several other forms are known.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a covalent bond in which two pairs of electrons are shared between two atoms