A disguise is something you put on so no one recognizes you. It also can be used as a verb. You can disguise yourself with a wig and mustache; that's a great disguise.
Disguise can be used anytime you're talking about concealing or hiding something. Most of the time we think of a disguise as something you wear, but you can also disguise your feelings. Criminals might disguise their intentions. You can also use the word to describe something that seems to be one thing, but turns out to be another. You missed the plane, but then the plane crashed. That's a blessing in disguise.