
A French seam is a style of seam used in the manufacture of garments from sheer and lightweight fabrics. The seam is made from a normal seam, which is then trimmed and turned to the wrong side and another seam made sandwiching the raw edges within it.
Found on
http://www.probertencyclopaedia.com/browse/PF.HTM

Completely enclosed seam. Used for sheer fabrics or for high couture.
Found on
http://www.thesewingdictionary.com/

A seam finish used for sheer and delicate fabrics, this method hides the raw edges in a neat double fold on the wrong side of the fabric. ie seam allowance is enclosed in the fold.
Found on
https://sewguide.com/sewing-terms-glossary/

a seam in which the raw edges of the cloth are completely covered by sewing them together, first on the right side, then on the wrong.
Found on
https://www.infoplease.com/dictionary/french-seam

with wrong sides together stitch your seam, turn wrong sides out (i.e. right sides together), press (optional) and restitch the seam, using a slightly larger seam allowance. This results in a neat seam with no raw edges to finish.
Found on
https://www.thesewingdirectory.co.uk/sewing-glossary/
No exact match found.