The word “worsted” is a derivative from the English city Worstead, where a high-quality woolen yarn was spun around 1250-1300. While the term worsted no longer refers to wool specifically, it still describes a medium-thickness yarn.
The Craft Yarn Council designates worsted weight yarn as “4” or "Medium".This yarn typically knits 4-5 stitches per inch in stockinette on a US 7-9 needle, and approximately 2.75 - 3.5 single crochet stitches per inch on a US I(9) to K(10.5) hook.
A 100 gram worsted weight hank will have approximately 220 yards.