Meaning of Selvage

The term selvage actually comes from the word "self-edge" this term has been around in the fabric world for a very long time because every fabric has a self edge or selvage. How does a fabric get salvage? Once the fabric is woven or knit it gets a finishing edge so that it doesn’t unravel later.
The selvage can be spotted running on either side of the fabric and is created by looping the threads back on themselves. What this does is it secures the fabric, creates an edge so that later the fabric stays tangled and intact. The selvage is the thin strip that is no wider than 3/4" and can be located at the outer edge of the fabric.

Selvage in denims

Selvage denim in actuality refers to the way in which the fabric has been woven, it should not be in any way confused with the way it has been washed. Selvage denims are woven in a special way with a continuous thread using very narrow loom, these are called "shuttle looms." This is the real key to creating the salvage edge. These looms weave the fabric in narrow width, only then, when the pattern is cut, the selvage can be included as the inner finished seam edge. This process makes the fabric stronger and that is why selvage denims are tougher and more long lasting than regular denims. If you compare the inside seams of a pair of selvage denims with a  regular denims the difference will be quite evident. This photo will explain it a bit better.
As you can see, the selvage pair has a red strip that runs along the seam edge. This red strip isn’t always the same colour, it may be brown, yellow, or green but red is the most common colour. Now, usually Selvage denims signify high quality which is primarily because of a specific stitch, but that’s not always the case. There are a various other factors that should be considered. Therefore it is crucial to ask pertinent questions, to check labels and lastly, be aware of these existing factors before you jump in to invest.