The adjective delinquent describes something that is past due or people who are negligent in doing their duty. If you are delinquent in paying your delinquent library fines, you won't be able to check out any more books.
You may have heard the term juvenile delinquent, which refers to a young (juvenile) person who gets in trouble, often with the law, but people of any age can be delinquent. A delinquent landlord is one who doesn't make repairs. A delinquent tenant is one who does not pay his rent.