emacs hyper key

[Thr4wn]

First of all, what actually IS the emacs hyper key? the emacs meta key
seems to just be mod1, but I can't seem to figure out what emacs will
interpret as the hyper key. right now, my left-windoze button is
assigned to be Super_L. I tried mapping Super_L to mod1 (whereupon
emacs interpreted it as meta, and I could use it just like meta). Then
I mapped Super_L to mod2, mod3, mod4, and mod5 (making sure that I
removed the previous binding each time); emacs acted like it did not
even know that button existed (ie after executing C-h k  , pressing
'a' returned binding for 'a'  and pressing L-Windoze button and 'a'
also returned the binding for 'a' (self-insert)).

Looking back over some old .emacs file I have, I used define-key but
the KEY arguments were things like [166...], but I do not even
recognize that notation anymore and I don't think that notation works
across different computers.

so...

what does emacs interpret as hyper?
what is that other notation I used in define-key?


I have a more recent version of Debian.