Flat seam?

What is and how do you do, a flat seam?

I’m currently stuck on sewing up my rowan movie star dressing gown. The book says

" Backstitch seams, except when stitching collars, for which use flat seam"

What is a flat seam? I can’t seem to find it in my books or on this site. Could someone please help because I can’t finish without it :pout:

hope everone’s having a good weekend x

Maybe an edge-to-edge seam?

Thank you for that. Last night I finally got the arms and side seams sewn up. HOORAY! :cheering: Just the collar to sew on, which I will do today, and 5 meters of border to knit up :verysad: