This stitch is used for joining together stitches that are on two separate knitting needles. It is similar to a 3-needle bind off.
I’ve included two variations: k2tog-fb, where you simply knit together one stitch from the front needle, and one stitch from the back needle. As well as k2tog-f&b, where you k2tog two stitches from the front needle, plus k2tog two stitches from the back needle, plus knitting together those two k2togs.
k2tog-fb
Insert right needle into first stitch on front needle as if to knit and first stitch on back needle as to knit and knit them together.
k2tog-f&b
Go into 2 front ndl sts as to k2tog then go into 2 back ndl sts as to k2tog and k2tog-fb. 2 sts off each ndl become 1 st. (-3 sts)