Goroutines use thread-per-core but run stackful fibers on top of that. (A similar model is sometimes known as "Virtual Processors" or "Light-weight processes".) This is unlike the use of stackless async-await in other languages. This peculiar use of fibers in Go is also what gets in the way of conventional C FFI and leads to quirks like cgo.
I'd love to see a resource that highlights these all on a table across programming languages as well as the associated strengths and weaknesses of such threading & concurrency models.
I usually just say that Go implements "userspace threading", since that's really what it is. Some early, pre-pthreads, implementations of Linux threads worked the same way as Go does and they usually called such implementations "M:N", to indicate M userspace threads mapped onto N kernel threads, so "M:N" is a good descriptor too.
IIUC it can, sometimes, avoid a kernel transition when it knows it can schedule the recipient of a message, but I believe that golang creates a threadpool for running goroutines on platforms that use thread primitives.
