This is the 2098th most frequent Korean word.
없습니다
"없습니다" means "does not exist" or "there is none."
없습니다 is used here to indicate the nonexistence of '약속' (appointments) for the subject '내일' (tomorrow).
내일은 약속이 없습니다.
I don't have appointments tomorrow.
없습니다 conveys the lack of availability of '우유' (milk) in the '가게' (store).
그 가게에는 우유가 없습니다.
That store doesn't have milk.
없습니다 expresses the absence of '돈' (money) in the '지갑' (wallet) as of now.