This articles is a fantastic, real world overview of cooperative and preemptive multitasking. Note that coroutines and fibers are essentially equivalent because they can be implemented, each with the other[1]. Unfortunately this thread (up to now) has been simply language tribal-ism. Helps if everyone is on the same page with respect to technical terms before that all starts.

[1] https://stackoverflow.com/a/3325985/2561675