CO stands for cast on, which is the foundational step in knitting where the initial loops of yarn are placed onto the needle. The method chosen dictates the elasticity and appearance of the garment's edge. Knitting patterns use this abbreviation to specify the starting stitch count, often followed by a number indicating how many loops to create.
Heard on the job
The pattern says to CO 64 stitches using the long-tail method for a stretchy cuff.