Unix: what modifier key does "M-" refer to (e.g. M-C)

Question

I'm trying to do a case-sensitive search in Nano. The help menu at the bottom of the screen says I can toggle case-sensitivity by typing M-C.

^G Get Help         ^Y First Line       ^T Go To Line       ^W Beg of Par       M-J FullJstify      M-B Backwards
^C Cancel           ^V Last Line        ^R Replace          ^O End of Par       M-C Case Sens       M-R Regexp

I'm not sure how to do this. Does M- refer to a modifier key that should be held while I type C? Or does M- mean I should press some key or key combination before hitting C?

Answer 1

M refers to the meta key, which is not present on most keyboards. (Its use in software is for primarily historical reasons.) Usually, the meta key is emulated by another key on your keyboard. On Windows and Linux, it is usually the Alt key. On Mac OS X, that key (aka Option) already has other uses, and so Escape is used instead.

Answer 2

Esc

For instance, if you wanted to go to the end of the file press

Esc then /

You don't need to hold down Esc as if it were Shift.