DK (double knitting) weight is a light-medium yarn (weight category 3) that sits between sport and worsted. It typically knits to about 5–6 stitches per inch and is popular for garments, baby items, and all-season projects.
DK yarn drapes more softly than worsted and gives finer stitch detail, which is why so many sweater and shawl patterns are written for it. It's a versatile middle ground when worsted feels too heavy and fingering too slow.