Yarn that is of uneven width, either because it has been spun to include supplementary short lengths of fibre at random intervals,, or because the fibres are of lesser quality and of shorter lengths than those that produce the finest yarns.
Slub threads or yarns can be used singly in either the warp or the weft, or in both. Dupion silk is the best-known slub weave and comes in a range of qualities; as a run of the mill cloth it’s good value with all of the properties of silk for the price of cotton.