The optimum twist is a term used in spun yarns, to describe the number of twists that gives the maximum breaking strength or the maximum bulk at strength levels acceptable for weaving or knitting.
S-Twist Yarn is a left-handed twisted yarn. See Z-Twist.
Singles yarn is the most simple strand of textile material suitable for operations such as weaving and knitting. A singles yarn formed from fibres with more or less twist; from filaments with or without the twist.
Weft or filling is a term used to describe the lengthwise, selvedge to selvedge horizontal, yarns carried over and under the warp.
Z-Twist is a term used to describe a right-handed twisted yarn, in contrast to S-Twist.