A Puerto Rican woman used to come into the bar to complain about her boyfriend, Hector. Shed get a little tipsy, look at me sincerely and say with spite, "That Hectorrr, heese a pee-jone!" and her tone would become gentle, and shed say to me, "But you know what you are? Yor an EEgle."

A coroutine is a control-flow feature that lets you arbitrarily suspend and resume a thread of control. They make it possible to build simple easily-understood systems around asynchronous I/O that would otherwise require complex state machines.