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.

Answer 1

I do not know for nano, but for emacs, M- stands for the Meta key, which can mean pressing the Alt key simultaneously with the letter key or by pressing Esc key before the letter key. Alt generally only works when using an X version of the application, so when using a dumb terminal, only Esc will work.