
A run and fell seam is a seam made on the right side of the garment, comprising a normal seam, to which one side is trimmed and the other side turned over the trimmed side and pressed under and the whole seam then topstitched on the right side. Run and fell seams are typically used in garments made of denim.
Found on
http://www.probertencyclopaedia.com/browse/PR.HTM

With wrong sides together, stitch a straight seam, 5/8″ from edge. Trim one seam allowance to 1/4″ and press seam open with both seam allowances to one side with wider seam on top. Fold this wider allowance over trimmed edge and top stitch down along fold. Used in denim jeans.
Found on
https://www.thesewingdirectory.co.uk/sewing-glossary/
No exact match found.