pointer vs handles in C (are the terms used to convey separate things?)

A handle is an old and revered concept.

A cookie is much the same thing. Or a GUID. Or a ticket to retrieve your car from a car park, or your coat from a fancy restaurant, etc.

Its any unique value that when presented back to the issuer can be used to track back to the actual thing referred, by whatever opaque mechanism the issuer wants. You may or may not know anything about that process, nor what the underlying thing is, exactly (only conceptually).

It was heavily used by Windows, but it is certainly not unique to Windows.

You would not normally use "handle" to mean "pointer to struct." Handle is more like "token" than like "pointer." It refers to something - file, system resource, memory, state-snapshot, etc. But what-exactly-it-is is based on the context of the handle itself (i.e. who issued the handle).

Handles were also used heavily in early filesystem programming in K&R C.

I use the word handle to mean a pointer that points to an "object" that represents a resource - often an OS resource, whereas a pointer just points to some memory. If you have a handle to something, you shouldn't try to read and write bytes into it directly, but manipulate it through provided methods.

Often handles are implemented as an opaque void *, which is further encouragement not to try to directly dereference it.

The term handle generally means some opaque value that has meaning only to the API which produced it. In Win32, the HANDLE type is either a pointer in kernel memory (which applications cannot access anyway) or an index into some kernel-internal array.