Dry or raw denim (contrasted with "washed denim") is denim that is not washed after having been dyed during production.
Over time, dry denim will usually fade, which is considered desirable by some people. During the process of wear, fading will usually occur on those parts of the article that receive the most stress. On a pair of jeans, this includes the upper thighs, the ankles, and the areas behind the knees.
After being made into an article of clothing, most denim articles are washed to make them softer and to reduce or eliminate shrinkage (which could cause the article to not fit properly after its owner washes it). In addition to being washed, "washed denim" is sometimes artificially distressed to produce a "worn" look. Much of the appeal of artificially distressed denim is that it resembles dry denim which has faded. In jeans made from dry denim, such fading is affected by the body of the person who wears them and by the activities of their daily life. This process creates what many enthusiasts feel to be a look more "natural" than artificially distressed denim.
To facilitate the natural distressing process, some wearers of dry denim will abstain from washing their jeans for more than six months. Most dry denim is made with 100% cotton and comes from several different countries. In particular, the United States, Zimbabwe and Japan are popular sources of cotton for making raw denim.
Dry denim also varies in weight, typically measured in by the weight of a yard of denim in ounces. 12 Oz. or less is considered light denim, 12 Oz. to 16 Oz. is considered mid-weight, and over 16 Oz. is considered heavy weight. Heavier denim is much more rigid and resistant to wear, but can also take more wears to break in and feel comfortable.