I always get confused around this and it seems to depend on specific keyboard and software. It seems to mostly be Alt, sometimes Alt Gr, and sometimes the Windows key. But I do remember using Meta to mean Alt when I was setting things up in Ubuntu maybe ten years ago.
I think Super and Meta are the vendor independent terms.
Ctrl - Ctrl - Ctrl
Super - Windows - Command
Left/Right Super - ?? - Open/Close Apple
Left Meta - Alt - Option
Right Meta - Alt Gr - Right Option?
Anybody able to fill the gaps?
Approaching an Apple keyboard for the first time, I naively thought Command would be Ctrl and was quite confused, since there also is Ctrl. But once you start a terminal it became quite clear that this was not the case. This is quite neat, it directly solves the SIGINT,SIGSTOP / Copy, Ctrl-D? confusion. Also having these operation as OS command means that all programs support them.
But, the meta key already exists and on Windows it is the Windows key. We're going around in circles.