The side address of any structure or property refers to the house numbers assigned to it along any side other than the main address side. This normally applies to side entrances, and especially to stores and similar tenants with street frontage which do not share the main address(es).

An address is a locator and not a property of the building. Streets are renamed and renumbered while the building stands, so an address is current rather than permanent and an old one stays valid for the period it applied.

A building with several entrances usually has several addresses. One of them is the main address and the others are recorded beside it rather than replacing it.

An address is not a position. Two buildings can share one address, and a large site can have an address on a street it does not touch, so the address does not locate the building on the map.