Coroutine is a routine which can yield. Coroutines are typically scheduled cooperatively (=non-preemptively). Coroutines are similar to threads, although threads are typically scheduled preemptively (scheduler pre-empts=forces execution to pause and yield, even without yield in the language)

Asynchronous operations are not the same as parallel or concurrent. Asynchronous simply means that we do not want to block our flow of execution(Thread) or wait for the response until certain work is done in full. But the way we implement Asynchronous operations decides whether they are (running) as parallel or concurrent. So parallel and concurrent are two implementations of asynchronicity of tasks.