This word has always confused me! Thank you to Wikipedia for this info.
According to the Craft Yarn Council, the term “Worsted Weight”, also known as “Afghan”, “Aran”, or simply “Medium”, refers to a particular weight of yarn that produces a gauge of 16-20 stitches per 4 inches of stockinette, and is best knitted with 4.5mm to 5.5mm needles (US size 7-9).
Worsted wool fabric is typically used in the making of tailored garments such as suits, as opposed to woollen wool which is used for knitted items such as sweaters
The essential feature of worsted yarn is straight, parallel fibres. Originally, long, fine staple wool was spun to create worsted yarn; today, other long fibres are also used.
Many spinners differentiate between worsted preparation and worsted spinning. Worsted preparation refers to the way the fibre is prepared before spinning, using ginning machines which force the fibre staples to lie parallel to each other. Once these fibres have been made into a top, they are then combed to remove the short fibres. The long fibres are combined in subsequent gilling machines to again make the fibres parallel. This produces overlapping untwisted strands called slivers. Worsted spinning refers to using a worsted technique, which produces a smooth yarn in which the fibres lie parallel.Examples of Worsted Wool