A cluster (no abbreviation) is a set of crochet stitches that you work across an equal number of stitches and join together (or cluster) at the top, forming a triangle shape that resembles an upside-down shell stitch. Many crocheters use this stitch combination in conjunction with shells.
What does CS mean in crochet?
The Camel Stitch (CS) is where you work a Half Double Crochet (HDC) in the Third Loop of the previous row. When working in the round, like hats or ear warmers, the third loop is found behind the top loops that you normally crochet in. This pushes the top loops to the front of your work like a braid.