An ordinance is a local law. Many cities have recently passed ordinances making it illegal to smoke indoors or mandatory for pet owners to curb their dogs.
Ordinance can also mean the act of making someone a priest. In both senses, it means a direction or command coming down from a higher authority or an official conference. If you break an ordinance, you'll likely be fined rather than jailed. Remember that an ordinance is a rule meant to keep things in order.