wyib or with yarn in back
This is telling you where your yarn should be before performing the next technique or stitch. Wyib or with yarn in back refers to the location of the yarn vis-a-vis the needles, so whether it is wrong side or right side it is always in relationship to the needles.
Working on the right side: wyib or with yarn in back places the yarn is behind the needles, on the wrong side.
Working on the wrong side: wyib or with yarn in back places the yarn behind the needles, on the right side.
See also: wyif or with yarn in front