What it says on the can... you have a group of men who do comedy. They've maybe been at it together since university or shortly afterwards. If they "do" women as part of their sketches or routines, it's generally as grotesques played by the boys in drag. But after a while something is mising. They come to realise it might be glamour, or somebody to play "straight" female roles. So they look around for an (ideally) attractive woman to join the gang, an actress who can do comedy, but not so well that she overshadows the boys...
Named for Carol Cleveland, the ex-Bunny Girl who became the seventh, distaff, Python, and who provided most of the glam when the script called for it. Later on, other female parts were also played by Connie Booth, of course (she was the first Mrs Cleese). And we are talking prolonged speaking parts here: Python did use other female performers, but in silent parts.)
Live TV: (and trope namer)
Subversions et c: