Abrash
Gentle horizontal bands of slightly different tone across a rug, caused by small differences between dye batches. In a hand-dyed rug it is a mark of authenticity, not a flaw.
Abrash is the gentle horizontal banding you see when the tone of a color shifts slightly across a rug. It happens because yarn is dyed in small batches over an open fire, and no two batches come out exactly alike. Woven together, those small differences leave soft bands.
It is often mistaken for a fault. It is the opposite: a sign that the wool was hand-dyed in a living process rather than colored to one flat machine value. It should not be confused with loom-tension irregularities, which affect the geometry, not the color, and which come from the warp rather than the dye pot.