A tailcoat is a knee-length coat characterised by a rear section of the skirt (known as the tails), with the front of the skirt cut away.
The tailcoat shares its historical origins in clothes cut for convenient horse-riding in the Early Modern era. From the 18th century, however, tailcoats evolved into general forms of day and evening formal wear, in parallel to how the lounge suit succeeded the frock coat (19th century) and the justacorps (18th century).
Thus, in 21st-century Western dress codes for men, mainly two types of tailcoats have survived: Dress coat, an evening wear item with a squarely cut-away front, worn for formal white tie Morning coat (or cutaway in American English), a day-wear item with a gradually tapered front cut away, worn for formal morning dress
In colloquial language without further specification, "tailcoat" typically designates the former, that is the evening (1) dress coat for white tie.
History
Shadbelly
In equestrianism, a variant called a shadbelly is still worn in certain disciplines in its eighteenth-century role as daytime formalwear. It is basically a form of dress coat which is closer in cut to the early nineteenth-century style worn by Beau Brummel than to the modern version worn with evening formal dress. The male version of the shadbelly is often called a "weaselbelly".
Levée dress coat
This is a type of dress coat traditionally worn with court dress, until the mid-twentieth century. It was made of black velvet and traditionally worn at court, levées, and evening state parties by those who did not wear uniforms. A version made of black barathea was also worn as diplomatic dress.
It was single breasted with a stand-up collar, with plain gauntlet cuffs, and two three-pointed flap pockets on the waist seam. It had six metal buttons at the front, and two decorative buttons at the back. The body of the coat was lined with black silk, and skirts with white silk. It was worn with breeches, black silk hose, white bow tie, white gloves, and court shoes (pumps) with steel buckles. The front of the coat was cut away squarely like a standard dress coat.
Military coatee
From c. 1790 until after the Crimean War, a red tail coat with short tails, known as a coatee, was part of the infantry uniform of the British army. The collar and cuffs were in the regimental colors and the coats had white braid on the front. Elite light infantry units like the 95th Rifles were issued short green coats to provide camouflage and ease of movement.
The Americans issued a similar uniform in dark blue to enlisted men during the War of 1812. This remained in service until 1833 when it was replaced with a shell jacket. Officers continued to wear tail coats until after the Mexican War when frock coats became the standard field wear. By the time the M1858 uniform was introduced tail coats had been relegated to full dress.
The Royal Navy had an elaborate hierarchy of tailcoats for the officers, allowing further buttons and gilding according to rank and seniority. These were single-breasted for junior officers and double-breasted for those with the rank of lieutenant and above.
Highland coatee
This is worn with Highland dress, and has a square cut away front like a dress coat, but the tails are cut significantly shorter.
Footman's coat
This was worn as livery, a servant's uniform. It was knee length with a sloped cut-away front like a morning coat. It was single breasted with a stand-up collar and gilt buttons. There were three-pronged side pockets similar in style to the levée dress coat.
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.