If you do Ctrl + G in nano text editor to read the list of shortcuts, you will encounter some shortcuts staring with ^ caret symbol while others start with M-. At first glance, you might think thats the letter M on your keyboard but actually it is a different key that was found on older keyboards called the meta key.

Since modern keyboards dont have this key. The Alt key in windows performs the same as meta key while the Esc replaced it in MacOS.