Also known as Centered Double Decrease, or Central Double Decrease.
It is a double decrease that reduces 3 stitches down to 1 stitch. As with other decreases, one stitch will remain visible when decreasing while the other 2 stitches remain hidden behind the main stitch. The CDD is a vertical decrease in which the two stitches adjacent to the center stitch are hidden behind the center stitch. The first and the third stitch merge into the center stitch creating a vertical center column/ridge.
LOOM KNIT 