Yarn is a long continuous length of interlocked fibres, used in sewing, crocheting, knitting, weaving, embroidery, ropemaking, and the production of textiles. Thread is a type of yarn intended for sewing by hand or machine. Modern manufactured sewing threads may be finished with wax or other lubricants to withstand the stresses involved in sewing. Embroidery threads are yarns specifically designed for needlework. Yarn can be made of a number of natural or synthetic materials, and comes in a variety of colors and thicknesses. Although yarn may be dyed different colours, most yarns are solid coloured with a uniform hue.

Sewing is the craft of fastening or attaching objects using stitches made with a sewing needle and thread. Sewing is one of the oldest of the textile arts, arising in the Paleolithic era. Before the invention of spinning yarn or weaving fabric, archaeologists believe Stone Age people across Europe and Asia sewed fur and leather clothing using bone, antler or ivory sewing-needles and "thread" made of various animal body parts including sinew, catgut, and veins.