A k1-fb increases 1 stitch to 2 stitches (an increase of 1 stitch).
To work the k-fb (knit into front and back legs)
First knit into the stitch on the left needle and without removing the original stitch from left needle, twist the right needle and knit into the back leg of stitch. With 2 new stitches on the right needle, remove the original stitch from the left needle.
Note: When working this type of increase a small purl bump will appear at the base of the stitch knit into the back leg; this cannot be avoided.
Same as k-fb or kfb.