What is a reverse SSN?

Excuse me, could you please clarify what exactly is meant by the term "reverse SSN"? I'm familiar with the concept of a Social Security Number, or SSN, which is a unique nine-digit identifier issued by the United States government to its citizens and certain residents. However, I'm not sure how the term "reverse SSN" fits into this context. Is it a reference to a specific type of fraud or identity theft? Or is it perhaps a term used in a different context altogether? I'd appreciate any clarification you could provide.