What is the cast on edge?
Picking Up Stitches: Cast-On or Bound-Off Edge
Picking up stitches is a way to add new stitches to an already finished bit of knitting–along the sides for a buttonband, perhaps, or at the neckline for a collar. You can add stitches to any edge: a cast-on edge, a bound-off edge, or the side edges.
Can you unpick cast off stitches?
If you don’t like the look of your bind-off, or if you did it too tight, you can always undo it. Just work back, one stitch at a time, removing the bind-off and putting the stitch back on your needle.