M-x ispell to spellcheck. When I finished, on the mini buffer a sentenced flashed quickly: "You can use
s-:" or something like that. What does
s-: stand for?
I am not sure for Macs, but on GNU/linux or Windows
s stand for the super/Windows key (usually left of the spacebar somewhere between Ctrl and Alt). Of course
: stands for the colon (usually Shift-semicolon), so here you would have to press super+shift+(semi)colon simultaneously.
C-h w ispell RETto find out to which key(s) the command
ispellis bound to. Maybe there is another one that is more convenient/accessible on MacOS.
s-:is listed. It's first time I see a binding for super key.
emacs -Q? If not, some init file (platform, or site, or personal) is probably defining it.