The term threadbare, in the flooring industry, describes a carpet or (more likely) a rug which has lost so much of its face yarn that the carpet or rug is wearing down to the backing. After a large percent of the carpet's nap or rug's face fibers have broken free and been vacuumed, the rug or carpet becomes thinner, splotchy, and seemingly bold. The net result is an overall shabby appearance.
Cause. In some rare cases, a rug or carpet may become threadbare due to chemical exposure (e.g., a wool yarn dissolved by exposure to bleach or a nylon yarn brittle by exposure to a strong acid). Most often, a rug or carpet becomes bare as surface fiber is simply worn away by foot traffic over a long time. Most building owners will not retain carpet long enough for the carpet to become threadbare. Therefore, threadbare deterioration most frequently observed with rugs.
Avoid. You can avoid having a threadbare rug by regularly rotating or relocating your rug.