Plain English Meaning
Fuel tanks built into the engine housings on the wings of a twin- or multi-engine airplane. Their position out on the wings means burning fuel from them shifts the airplane's left-right weight balance and changes the loads on the wing structure.
Full Definition
Fuel tanks installed inside the nacelles of a multiengine airplane — the streamlined housings that surround each engine. Because they sit out on the wings away from the airplane's centerline, fuel burned from nacelle tanks has a noticeable effect on the airplane's lateral (side-to-side) balance and on the bending loads carried by the wings.
Context Anchor
Seen in weight-and-balance , , and for some multi-engine airplanes.