dress coat

from The Century Dictionary.

• noun A coat worn by men on occasions of ceremony; especially, a coat fitting tightly, and having the skirts cut away over the hips. See coat, and full dress, under dress.

from the GNU version of the Collaborative International Dictionary of English.

• A coat with skirts behind only, as distinct from the frock coat, of which the skirts surround the body. It is worn on occasions of ceremony. The dress coat of officers of the United States army is a full-skirted frock coat.

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

• noun A usually black evening tailcoat worn by men as part of the white tie dress code.