The green button was originally “zoom” which, to Apple, meant “adjust this window to its content, or revert to the previous size.” Some apps implemented zoom as

The green button was originally “zoom” which, to Apple, meant “adjust this window to its content, or revert to the previous size.” Some apps implemented zoom as maximize, but that was not The Apple Way®. Their full-screen-window-gets-its-own-desktop-space was added later.