I'm using the definition from back in my Unity programming days.
So I think your description is right, it's very like async/await which are coroutines by my definition, just the resumption criteria is "the next tick after something happened". My implementation here does 1 of 2 things. An update coroutine is being called back by requestAnimationFrame - so guaranteed every tick presuming the system isn't under heavy load. js-coroutines also does requestIdleCallback to run things in the "gaps" - in this when you yield it checks how much time is left and if there is enough, you get to go again straight away.
In Unity coroutines are called every game loop (so the Unity equivalent of requestAnimationFrame). I've just built a library to use that and the other principle, in conjunction with generator functions.
My implementation of both allows for termination because the promise returned by run or update has a terminate method that will stop it on the next time it's called.
I detail the actual code that runs the coroutines and a bit of a broader description in this article.
We're a place where coders share, stay up-to-date and grow their careers.
We strive for transparency and don't collect excess data.