Knitted fabrics are constructed by interlocking a series of loops made from one or more yarns, with each row of loops caught into the preceding row. Loops running lengthwise are called wales, and those running crosswise are courses. Hand knitting probably originated among the nomads of the Arabian Desert about 1000 bce and spread from Egypt to Spain, France, and Italy. Knitting guilds were established in Paris and Florence by the later Middle Ages. Austria and Germany produced heavily cabled and knotted fabrics, embroidered with brightly coloured patterns. In the Netherlands, naturalistic patterns were worked on fabric in reverse stocking stitch, and several Dutch knitters went to Denmark to teach Danish women the Dutch skills. The craft of hand knitting became less important with the invention of a frame knitting machine in 1589, although the production of yarns for hand knitting has remained an important branch of the textile industry to the present day.
Knitted fabrics were formerly described in terms of the number of courses and wales per unit length and the weight of the fabric per unit area. This system is limited, however, and there is a shift to use of the dimensions and configuration of the single loop, the repeating unit determining such fabric characteristics as area, knitting quality, and weight. The length of yarn knitted into a loop or stitch is termed the stitch length, and in a plain knitted structure this is related to the courses per inch, wales per inch, and stitch density. The two basic equilibrium states for knitted fabrics are the dry-relaxed state, attained by allowing the fabric to relax freely in the air, and the wet-relaxed state, reached after static relaxation of the fabric in water followed by drying. Source: https://www.britannica.com/topic/textile/