This stitch combines a decrease (ssk) with a dropped stitch.
The first step in the process is to slip 1 stitch knitwise.
Now we drop the next stitch off the needle. Note that it will only unravel as far as the yarnover from several rows below.
Now we slip the next stitch knitwise. This will become the second stitch for the ssk.
Knit these 2 stitches that were slipped together to create the decrease.
This is what your Drop Stitch Decrease will look like, stitches from both sides of the dropped stitch are combined together into a ssk decrease with the stitch in the middle dropped.