Completely off-topic, but I frequently see this type of word correction formatting online but have no idea where it's from.

Is this a type of emacs/vim find & replace shortcut, or is it just something that people have picked up on the internet and run with?

Yes, it is used in vim and sed (and probably more). s is for "substitute". g means global, substitute each occurrence, not just the first.

Thanks! I've been scratching my head on that one for a while.