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.