Valve Trim is collective name for the internal elements of the valve. The Valve Trims are directly exposed to the process fluid except the body, bonnet, flanges and gaskets. As per API code Trim is defined as the seating surfaces of the body, disc, disc to shaft connection hardware (e.g., keys, pins, screws, etc.) and any internal fasteners that are in contact with the process fluid.
The Plug, seats, stem guides, bushing and cage are some of the parts we can say Valve trims.