[colanderman]

Terminology nit: "file descriptor" is the reference itself. "Open file description" is the thing referenced. dup(2) and fork(2) create new file descriptors which reference the same underlying open file descriptions.

[zbentley]

Correct, sorry! My phrasing was off-the-cuff and less than precise.

File descriptor = reference/pointer-ish thing.

File description = referenced data.

close(2) = decrement refcount to description by closing descriptor; actual destruction of the file's open-ness doesn't happen until refcount == 0.