In article , Iris Cohen
writes
Judd et al say that they're (walnuts) drupes.

Now I am really confused. Does that mean they come in a fleshy outer covering,
like the almond, and what we call the nut is just the seed? I seem to recall

That appears to be more or less the case (pace technicalities in the
definition of seed); do a Google image search for walnut fruits.

that some of that group, like the hickories, have a sort of outer husk. So
which are the true nuts? And what do you call a cashew?

Judd et al give hazel, sweet chestnut, oak and beech, plus some tropical
genera, as examples.
--
Stewart Robert Hinsley