Question on bind off

*K2, k2tbl. With yarn in back, slip worked 3 sts from RHN back to LHN and repeat from *

Not sure what this decrease is? Can someone help?

What it is telling you to do is to knit two stitches then knit two stitches together through the back loop. Then it wants you to slip the 3 worked stitches from the right needle back to the left needle and repeat the process again. I hope this helps.

It seems like the pattern leaves out the together in the k2tog tbl instruction but I agree with trisha’s interpretation.
Which pattern is it? Can you give us a pattern name or a link?

It looks like an I-cord bind off similar to the one I’ve been doing. So the k2tbl should actually be K2tog tbl. It forms an I-cord attached to the top of the work.