full moon

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

• noun The phase of the moon at which the moon, as viewed from Earth, appears to be fully illuminated by the sun. The full phase marks the half-way point of a single revolution of the moon around the earth.
• noun The period of the month when such a moon occurs.

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

• noun The phase of the moon when it is in opposition to the sun.
• noun The moon when it is in opposition to the sun.

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

• noun the time when the Moon is fully illuminated