Flat Felled Seam
An enclosed reinforced seam frequently used where a little extra strength is desired, to reduce seam bulk, or for decorative purposes.
There are several ways of doing it, whichever one is the one you were taught or prefer to use, is the right one. (G)
Here are three of the most commonly used methods.
1) Sew a seam with the fabric wrong sides together. Trim one side of the seam close to the fabric. Fold the other side of the seam over the trimmed side, fold it under itself, and topstitch down.
2) Sew a french seam starting with right sides together. Press to the side. Topstich down.
3) Press a fold between 3/8 and 5/8s wide (as suits the project) along the seam edge of each section of fabric, pressing one fold to the right side of the fabric, and the other side to the wrong side of the fabric. Carefully nest the folds with the section pressed to the wrong side on top, and the raw edge of the fabric next to the pressed fold.Topstitch along the fold, flip and topstitch along the other fold.
These seem to me to be three different seam styles, but there it is.