A coroutine is an instance of suspendable computation.
It is conceptually similar to a thread, in the sense that it takes a block of code to run that works concurrently with the rest of the code.
However, a coroutine is not bound to any particular thread. It may suspend its execution in one thread and resume in another one.
以上这段话出自官网。介绍协程的基本概念和一些特性。
