Yarn; folded, doubled, plied

A yarn in which two or more single yarns are twisted together in one operation, e.g., two-fold yarn, three-fold yarn, etc.

Note: In some sections of the textile industry, e.g., the marketing of hand-knitting yams, these yarns are referred to as two-ply, three-ply, etc.

Textile Resource (http://www.textile.org.uk)