They mean async/await running over multiple OS threads compared to over one OS thread. You can also have threads running on one OS thread (Python) or running o

They mean async/await running over multiple OS threads compared to over one OS thread. You can also have threads running on one OS thread (Python) or running on multiple OS threads (everything else). Every language’s concurrency model is determined by both a concurrency interface (callbacks, promises, async await, threads, etc), and an implementation (single-threaded, multiple OS threads, multiple OS processes).