Worsted weight yarn is a medium-weight yarn that’s used in a vast range of patterns, from cozy sweaters to scarves, hats, and blankets. It’s one of the most popular yarn weights—easy to work with, and great for beginner knitters.
Worsted weight yarn is also called afghan yarn (see above re: blankets). Aran yarn is a sub-set of worsted weight yarn. If your pattern calls for aran yarn, keep an eye on your gauges and play with needle sizes until you get the gauge you need.