This is adding a reinforcing fabric strip to pockets which may be concealed. A welt pocket is also called jetted pocket. Found on https://sewguide.com/sewing-terms-glossary/
Turbulent flow of resin from an undersized gate or thin section into a thicker mold section, as opposed to laminar flow of material progressing radially from a gate to the extremities of the cavity. Found on https://www.teampti.com/glossary-of-terms/