Tailcoat
A tailcoat is a coat with the front of the skirt cut away, so as to leave only the rear section of the skirt, known as the tails. The historical reason coats were cut this way was to make it easier for the wearer to ride a horse, but over the years tailcoats of varying types have evolved into forms of formal dress for both day and evening wear. Although there are several different types of tailcoat, the term tailcoat is popularly taken to be synonymous with the type of dress coat still worn today in the evening with white tie. This dress coat, one of the two main surviving tailcoats, is a dark evening coat with a squarely cut away front. The other one is the morning coat (or cutaway in American English), which is cut away at the front in a gradual taper.
Types
Dress coat
A dress coat, sometimes called a swallow-tail or claw-hammer coat, is the coat that has, since the 1850s, come to be worn only in the evening by men as part of the white tie dress code, also known as evening full dress, for formal evening occasions. It is commonly referred to as just a tailcoat, but amongst tailors (both British and American) and dress historians it is traditionally called a dress coat to differentiate it from other types of tailcoats.