Question on a stitch I have never heard of

I was asked by a friend to gauge the difficulty of a pattern she found online, I looked at it and it is an old pattern from the late
1800’s. Looking through I found a stitch I have never encountered before, it is called a seam stitch, and it was used in a ribbing pattern (knit 1 seam 1) I have yet to figure out what this is and would like to get back to her asap, but I can’t figure out what the stitch is other than the fact that it cannot be a purl stitch. Can anyone tell me what it is and how to do it?

It could be just a stitch that’s designated as a `seam’ stitch; one that’s there in place of joining two pieces together. No notes or explanations in the pattern?

I found this link to a vintage pattern that is updated to a modern pattern. It includes “seam” stitches in the original pattern. By looking at how they updated the pattern it looks like they purl where the vintage pattern says “seam”:

Oh, it looks like they use seam stitch to indicated selvedge sts. Maybe. They have seam sts in the middle of the row…

Seam could mean purl? Look at the pattern as a whole not one word. Is it saying knit one seam one across? And then referring to this row as ribbing? And is it in a place where you would expect ribbing, like the wrist of a sleeve? Things like that can give you an idea. And there is no reason you have to do things exactly the way you are instructed.

If you scroll down to the updated pattern, the author is using purl to replace seam.