The cable k3tog, is a cabled decrease. It combines a knit three stitches together decrease, with a cable. First you rearrange the order of your stitches, and then k3tog.
k3tog – knit three stitches together
How to cable k3tog
Slip first stitch to right hand needle as if to knit. Put next stitch on cable needle and hold in front. Slip following stitch onto right needle as if to purl. Slip stitch from cable needle onto left needle. Then slip two slipped stitches from right needle to left needle. Finally, k3tog.