C-h w undo RET says "undo". Where is it?

[Marcin Borkowski]

Hi all,

Emacs tells me that `undo' is bound to several keys.  Personally, I use
C-/ almost exlusively, but C-h w undo RET says that it's also bound to
<undo>.  Where is that key?  More precisely, can anyone show me an
example of a keyboard (preferably a modern one, not a historical
curiosity) possessing such a key?

TIA,

-- 
Marcin Borkowski
http://mbork.pl