231 order.. I'd calll that a raised center decrease..
stick the crochet hook into stitch 2 and 1 (as if to knit.)
turn the stitches (and the hook!) and then stick it into the back loop of stitch 3
wrap yarn round hook and pull a stitch through. (stitches 1 and 3 will be 'sitting under stitch 2 (which will be RAISED and in center postition..
it should look like this top of this image (where there are several raised centered decreases in a row) (vs the double decreases in section below top)