How Different Kinds of Music Got Their Names

Jazz: Five men on the same stage all playing different tunes.
Jazz began as a West Coast slang term around 1912, the meaning of which varied but which did not refer to music or sex. Jazz came to mean jazz music in Chicago around 1915. Jazz was played in New Orleans prior to that time but was not called jazz.

Blues: Played exclusively by people who woke up this morning.
The phrase the blues is a reference to having a fit of the blue devils, meaning 'down' spirits, depression and sadness. An early reference to "the blues" can be found in George Colman's farce Blue devils, a farce in one act (1798). Later during the 19th century, the phrase was used as a euphemism for delirium tremens and the police.
Though usage of the phrase in African American music may be older, it has been attested to since 1912, when Hart Wand's "Dallas Blues" became the first copyrighted Blues composition. In lyrics the phrase is often used to describe a depressed mood.

World Music: A dozen different types of percussion all going at once.
The term became current in the 1980s as a marketing/classificatory device in the media and the music industry, and it is generally used to classify any kind of "foreign" (i.e. non-Western) music.

Opera: People singing when they should be talking.

Rap: People talking when they should be singing.
Although the word rap has sometimes been claimed to be a backronym of the phrase "Rhythmic American Poetry", "Rhythm and Poetry", "Rhythmically Applied Poetry", or "Rhythmically Associated Poetry", use of the word to describe quick and slangy speech or repartee long predates the musical form

Classical: Discover the other 45 minutes they left out of the TV ad.
The term classical music did not appear until the early 19th century, in an attempt to "canonize" the period from Bach to Beethoven as an era in music parallel to the golden age of sculpture, architecture and art of classical antiquity (from which very little music has directly survived). The earliest reference to "classical music" recorded by the Oxford English Dictionary is from about 1836. Since that time it has come into common parlance as a generic term denoting the opposite of light or popular music.

Folk: Endless songs about shipwrecks in the 19th century.
The word became colloquialized (usually in the plural "folks") in English in the sense "people", and was considered unelegant by the beginning of the 19th century. It re-entered academic English through the invention of the word folklore in 1846 by the antiquarian William J. Thoms (1803-85) as an Anglo-Saxonism. This word revived folk in a modern sense of "of the common people, whose culture is handed down orally", and opened up a flood of compound formations, eg. folk art (1921), folk-hero (1899), folk-medicine (1898), folk-tale (1891), folk-song (1847), folk-dance (1912). Folk-music is from 1889; in reference to the branch of modern popular music (originally associated with Greenwich Village in New York City) it dates from 1958. It is also regional music.

Big Band: 20 men who take it in turns to stand up plus a drummer.
A big band is a type of musical ensemble associated with playing jazz music and which became popular during the Swing Era from the early 1930s until the late 1940s. A big band typically consists of approximately 12 to 19 musicians and contains saxophones, trumpets, trombones, and a rhythm section. The terms jazz band, jazz ensemble, stage band, jazz orchestra, and dance band are also used to refer to this type of ensemble.

Heavy Metal: Codpiece and chaps.
The origin of the term heavy metal in a musical context is uncertain.
The first documented usage of the term to describe a musical style is in a May 1971 Creem review by Mike Saunders of Sir Lord Baltimore's Kingdom Come: "Sir Lord Baltimore seems to have down pat most all the best heavy metal tricks in the book."[27] Creem critic Lester Bangs is credited with popularizing the term via his early 1970s essays on bands such as Led Zeppelin and Black Sabbath.[28] "Heavy metal" may have initially been used as a jibe by a number of music critics, but it was quickly adopted by fans of the style.
The terms "heavy metal" and "hard rock" have often been used interchangeably, particularly in discussing bands of the 1970s, a period when the terms were largely synonymous

House Music: OK as long as it's not the house next door.
The origins of the term "house music" are disputed. The term may be derived from the name of a club called the The Warehouse, which was one of the nightclubs that became popular among the teenagers living in the Chicago area in the late 1970s and early 1980s. One of these nightclubs, The Warehouse was patronized primarily by gay black & Latino men , who came to dance to DJ Frankie Knuckles' mix of classic disco, European synthpop, new wave, industrial, and punk recordings. Knuckles released his dance tracks and mixes on the Traxx record label, which became known as house music.