Hi there and thanks for joining us. The phrase means that the void(s) in the piece (holloware) is filled with a cement-like resin to strengthen it. Silver is a very soft metal and needs reinforcement in many applications. It is also used to add weight to pieces like vases to keep them from tipping over, and those would normally be marked “weighted”. You frequently see “reinforced with iron rod” markings on tall silver objects.
Such markings show the maker is eithical and informing the user that the object is not solid silver through and through but contains another material.
Regards,
UV