Without additional context, it is difficult to determine what "31" refers to. However, based on the search results, it could refer to:

• Womens jeans size: According to the True Religion size chart, a womens jean size 31 has a waist measurement of 31.5 inches and a hip measurement of 38.5 inches.
• Mens jeans size: According to the BlitzResults jean size chart, a mens jean size 31 has a waist measurement of 31-32 inches and a hip measurement of 38-39 inches.
• Mens suit size: According to the Tradeinn size chart, a mens suit size 31 has a chest measurement of 31-33 inches.

It is important to note that sizing can vary between brands and countries, so it is always best to consult the specific size chart for the item in question.