If it's the plastic molding used in most RVs, it's called T-molding. It pushes into a kerf milled into the edge of the material you're covering.
curmudgeon: noun; a crusty, ill-tempered, irascible, cantankerous old person . . . .
79 27' Holiday Rambler Statesman, 78 32' HR Imperial, 85 36' HR Imperial 5th Wheel