Knitting in the stitch below blends two rows of stitches and create a deeper fabric. It is used in fisherman rib. It is easy to do, but can be confusing to correct a missed mistake.
I am using k1-blw because I use k1-b for k1-tbl. I think using k1-blw makes it clear that knitting is done into the stitch below.
Instructions usually read Row 1 [RS]: K1, *k1-blw, p1; repeat to last stitch, end k1.
Row 2: P1, *k1-blw, p1; repeat to last stitch, end p1.
To K1-blw:
Put your right needle into the knit stitch directly below the stitch on your left needle and continue to work a k1, moving the new stitch to your left needle. There will be two bars in the top of the new stitch: the stitch in the row below, and the stitch from the needle.
On the next row, knitting in the stitch below is worked into the stitch that was purled so now looks like a k1.
Videos
How to work k1-blw:
The hardest part is fixing a mistake:
