(1) A continuous-filament single yarn in which there is no twist
(2) A multi-fold yarn in which there is no folding twist.
Note 1 : Some fibrous yarns are described as twistless, since the fibres may be held together by adhesive temporarily e.g., until incorporated in fabrics. Varieties of core-spun yarn and scaffolding yarn have appeared with this description after solvent-removal of one component.
Note 2 : Zero-twist continuous-filament yams usually become twisted by over-end withdrawal e.g., from a pirn in a loom shuttle
Textile Resource (http://www.textile.org.uk)