Felled seam Wikipedia
Felled seam, or flat-fell seam, is a seam made by placing one edge inside a folded edge of fabric, then stitching the fold down. It includes a topstitched finish. It is useful for keeping seam allowances flat and covering raw edges.
The flat-felled seam is the type of seam used in making denim jeans, although it appears inside-out to reduce stitching. It is also used in traditional tipi construction.
There are flat-felled seams and lap-felled seams.