Bind off in pattern or “BO in patt” means binding off while continuing the knit/purl stitch pattern you’ve been using. Binding off in pattern continues the interaction of stitches by working them as a pattern row while binding off. Basically, it means to bind off your knits knitwise, and your purls purlwise.
Bind Off In Pattern
Work 2 stitches in pattern. *Use your left needle to bring the first worked stitch on the right needle over the second stitch worked and off the right needle. Work next stitch according to pattern and repeat from * to last stitch. Cut yarn and draw through last stitch.
Similarly to working a pattern as established and working pattern repeats, binding off in pattern can seem a bit confusing at first, though it gets significantly easier with practice.
See also cut yarn to pull through last stitch (bind off).
For more about about bind offs, see bind off or BO, Three Needle Bind Off (3-needle BO), Easy Ribbed Bind Off, JSSBO or Jeny’s Surprisingly Stretchy Bind Off, Yarn Over Bind Off – YO BO, decrease bind off.