Under the Building Act 1993 protection work is work that must be undertaken [by an owner who is proposing building work] to protect an adjoining property of a building site from proposed building works. It can be done on an adjoining property or on the building site where the building work is occurring, or both. An example of protection work is the shoring up of the adjoining property (which may include retaining walls and bored piers).
For more info visit the Victorian Building Authority website on the link here.