maiden name

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

• noun The surname that a girl is given at birth and that some women change when they marry.

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

• noun A married woman's original last name; her name when she was a maiden.

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

• noun a woman's surname before marriage