This abbreviation is from “Socks a la Carte 2”.
Used in the heel.
3 days I worked on it and didn’t figure it out,
First there is an error in the printed pattern.
Second, the wording is very odd. 2 professional ladies at my LYS, Mystic River, Mystic, CT. spend almost 3 hours trying to help me and get it right.
THEY DID and now I can finish the socks.

It was a toughy to be sure.

I saw a thread about this one on Ravelry. The consensus was you could do it as a regular ssk and it would probably come out okay.

I think I figured it out. You need to keep the same number of stitches so you do an SSK with the next stitch and the loop below the following stitch (the row below) then knit the stitch in the current row (the one above the loop you just knitted. I haven’t tried it on socks yet but it should work.