A beam axle is a rigid axle supporting non-driven wheels.

all moving axle parts are in a strong casing (beam) filled with oil

A shaft that does not transmit power but provides a means of fastening wheels to either, or both, ends.

A beam axle is a suspension system, also called a solid axle, in which one set of wheels is connected laterally by a single beam or shaft. A live axle is a type of beam axle in which the shaft (or shafts, since live axles, while connected to move as a single unit, are seldom one piece) also transmits power to the wheels; a beam axle that does not also transmit power is sometimes called a dead axle. Beam axles are commonly used at the rear wheels of a vehicle.