The Collaborative International Dictionary
Dress coat \Dress" coat`\ 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.
Wiktionary
n. A usually black evening tailcoat worn by men as part of the white tie dress code.
Usage examples of "dress coat".
He was dressed in a dark-green dress coat, knee breeches of the color of cuisse de nymphe effrayee, as he called it, shoes, and silk stockings.
As a lieutenant without influence or distinction, Pettigrew was only a captain by courtesy, not rank, and from the gray that streaked his hair and the rumfed belly that the rumpled, salt-stained dress coat refused to cover, the tiny Antelope was likely to be the only command he'd ever have.