Ctrl is Control (a keyboard command made by using that key in conjunction with another key i.e. Ctrl-C = copy.
Control was originally used to form control characters, ASCII characters 1-31 (Ctrl-A to Ctrl-Z plus a few others: Ctrl-[ and -], Ctrl-/ and a couple of others I forget). These represent characters that do not, in themselves, represent a visible symbol - things like backspace, new line, escape etc. are all control characters. Only later did they become a (different) set of GUI shortcuts.
Any Unix user will know plenty of these - Ctrl-A moves to the start of a line, Ctrl-E moves to the end, Ctrl-D deletes the next character, Ctrl-H the previous one (hence all the un^H^Hfunny '^H' jokes you sometimes see...
). Microsoft's cmd also supports some, but not all. Anyone who has used Telnet will know Ctrl-].
What's really annoying is when you're used to Unix and try using some of the commands you're used to in a GUI. Ctrl-W by convention deletes the last word you tried. In firefox it closes the current tab (without warning, as I discovered the first time I typed this...
)
Oh, FWIW, i've also heard Alt GR called "alternate graphics" (don't really know why) and a French person calling it "acute/grave" (although on my UK-English setup I can't work out how you use it for graves, Alt Gr-A gives the acute)