What is the “atom” data type?

Question

I have encountered the ATOM type in the Win32api and also in the Acrobat API there is ASAtom.

As far as I can tell, atoms are keys for a hash table usually

Answer 1

ATOM is a 16-bit Windows handle-like primitive. It's value is completely opaque to user-mode. It is not a pointer or an index.

typedef unsigned short ATOM;