What is contrafact?

Parker's style of composition involved interpolation of original melodies over existing jazz forms and standards, a practice known as contrafact and still common in jazz today. Examples include "Ornithology" (which borrows the chord progression of jazz standard "How High the Moon" and is said to be co-written with trumpet player Little Benny Harris), and "Moose The Mooche" (one of many Parker compositions based on the chord progression of "I Got Rhythm"). The practice was not uncommon prior to bebop, but it became a signature of the movement as artists began to move away from arranging popular standards and toward composing their own material. Perhaps Parker's most well-known contrafact is "Koko," which is based on the chord changes of the popular bebop tune "Cherokee," written by Ray Noble.[45]

Contrafact is a type of jazz composition where the composer takes the basic structure of a popular song, rearranges it and provides a new melody to the song. Charlie Parker was a jazz musician and composer who used this style of composition extensively. Some of the best known examples of Parker's use of contrafact are:
"Ornithology"- Based on the popular song "How High the Moon"
"Moose the Moose"- Based on the standard "I've Got Rhythm"
"Koko"-Based on the swing standard "Cherokee"