The response you give when you don't 100% want to say "Yes" but also don't want to say "No". "Sure" is the answer you use when on the fence about something, but is not an acceptable response to Y/N questions.
the quickest way to answer a question when not paying attention that usually doesn't include any thinking what so ever. also used in a very sarcastic way.
Ex. teacher- Jimmy are you going to be coming to detention today?
Jimmy- sure
MOM- i have to go to the store and then to the laundry matt and then bla bla bla bla bla ARE YOU LISTENING TO ME???
child- sure