male pattern baldness

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

• noun A progressive, diffuse loss of scalp hair in men that begins in early adulthood, depends on the presence of the androgenic hormone testosterone, and is caused by a combination of genetic and hormonal factors.

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

• noun a progressive loss of hair from the scalp in men caused by the presence of testosterone

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

• noun loss of hair on the crown of the head