A maintenance contract is an agreement under which a tradesperson regularly checks a set of installations, in this case locks, lock cylinders, deadbolts and door closers, and deals with their faults on terms agreed in advance.
They are usually requested by communities of owners, property administrators, businesses and owners with several rental homes, because they have the most locks in use and the least time to keep an eye on each one.
Before signing, check what it includes: how often the checks are done, which doors are covered, whether materials are extra and how emergencies are handled. Ask for everything to be put in writing. We discuss it under lock maintenance.