thread coated with wax, usually paraffin or beeswax
Waxed threads are typically used for hand sewing and in waxed-thread sewing machines.
Wax on thread can improve its strength, abrasion resistance, UV resistance, and appearance. The wax can also provide lubrication that improves the speed and smoothness of sewing, especially through tight holes in abrasive materials such as thicker or harder leathers.
These properties can be particularly important when hand sewing stitches, such as shoemaker stitch, where leading ends of thread, closest to the needles, pass through the material repeatedly, through every hole in a line.
Threads may be sold pre-waxed or waxed by hand or machine just prior to sewing.