What do you mean by liner?

By liner we mean material or object used as inner protective layer, lining, or insert inside something else to protect, contain, waterproof, insulate, or improve appearance or function, with many applications across industries. For example, by liner we mean plastic bag lining trash bin to hold garbage called bin liner, waterproof membrane lining pond or pool to hold water called pond liner, thin absorbent pad lining underwear for feminine hygiene called panty liner, cosmetic pencil lining eyes or lips called eyeliner or lip liner, fabric lining inside jacket or bag called clothing liner, metal or clay layer lining chimney called chimney liner, and large passenger ship traveling regular route called ocean liner. So by liner we mean inner layer that lines interior, whether for protection, containment, or decoration, serving as barrier or insert. So liner is inner layer, membrane, or product that lines something.