*G (Gastric): G-tubes are surgically placed directly into the stomach.
*NJ (Nasojejunal): NJ-tubes run from the nose to the intestines.
*GJ (Gastricjejunal): GJ-tube is surgically placed in the stomach, and tubing runs to the intestines.
*J (Jejunal): J-tube can be surgically placed directly into the intestines or into the stomach like a GJ-tube.
Source: Feeding Tube Awareness Foundation