Quarks are elementary particles that combine to form atomic particles. They were theorized by Murray Gell-Mann and George Zweig in 1964.
Originally they were pronounced “kwork” by Gell-Mann. He settled on the spelling of the particle when he read a verse in James Joyce’s Finnegan’s Wake:
“Three quarks for Muster Mark!
Sure he has not got much of a bark
And sure any he has it’s all beside the mark.”
While Gell-Mann continued to use the original pronunciation, the culturally-accepted form now rhymes with bark.
In order to make their calculations work, the quarks had to be assigned fractional electrical charges of 2/3 and -1/3. Such charges had never been observed before. Quarks are never observed by themselves, and so initially these quarks were regarded as mathematical fiction. Experiments have since convinced physicists that not only do quarks exist, but there are six of them. The different kinds are known as “flavors.”
The flavors of quarks are up, down, strange, charm, top and bottom.