What does XX mean?
The original name for Levi’s 501 jeans.
Heddels explains XX
The XX jean was the name of Levi’s 501 jeans before they were called 501. The name XX was derived from a notation used in price lists to mean “extra, extra strong,” and reflects the status of jeans as working wear. Levi’s XX jeans originally had only one back pocket, with a second back pocket added in 1901. The pants were renamed 501 in 1890 to refer to a specific lot number. In acknowledgment of these original jeans, Levi’s reintroduced the XX name in 2009.
Here is an example of Levi 501’s: