[Deathbyteacup]

A DMU is a form of railcar.

A form of railcar is a railbus, such as the Pacer, which is also considered a DMU. Many texts also refer to DMU's as railcars in the same sentence and vice-versa.

You could call a DMU a DMU or a Railcar, but I think when we have something that is a single coach with a cab at each end with no articulation, or more importantly, can't be used in multipul, then it would simply be refered to as a railcar.\

The only flaw in my perception which I have always held is the Silver Fern which you hold up as an example, since not only does it appear to articulate, it also appears to have couplers, so I fail to see why you would not class it as a DMU, unless it can't work in multipul with other units!