SSK stands for "slip, slip, knit" and is a knitting technique used to create a left-leaning decrease that reduces two stitches to one. To perform an SSK, you slip two stitches from the left needle to the right needle knitwise, one at a time, then insert the left needle into the front of these two slipped stitches and knit them together through the back loops. The result is a decrease that leans to the left. SSK is typically used on the right side of your work, while K2tog (knit two together) is used on the left side.