Until now we have talked about processes, from now on we will talk about resources , the things operated upon by processes. Can take resource away, use it for something else, then give it back later.
Examples are file space, terminal, and maybe memory.
This distinction is a little arbitrary, since anything is preemptible if it can be saved and restored. It generally measures the difficulty of preemption. Implication is that resources aren't easily preemptible. Implication is that resource is preemptible. That is, waiting for CPU time.