What does Belt Loops mean?
A series of loops around the waist level of denim that hold a belt and help to hold up the pants on the individual wearing them.
Heddels explains Belt Loops
In the twenties, belt loops were phased in to replace suspender buttons. Most jeans have five belt loops; however, some manufacturers such as Wranglers have seven for extra support. Wranglers’ belt loops are also extra-wide to allow for wider, Western-style belts. Some styles of jeans also have double belt loops with a smaller loop underneath the visible loop to allow for both thinner and wider belts, with thinner belts going through the inner loops and wider belts going through the outer loops.
Here is a picture of a belt loop: