I use poundcake as a synonym to spongecake. The ingredients and process are the same, with variations large enough between recipes to accommodate both. (Cupcake, chocolate cake, lemom cake, some apple cakes all use the same basic dough composition too)

Poundcake vary greatly beyond a "pound".

If anything, spongecake is more strictly defined, originally not using leveling agents, relying on the air bubbles introduced in the beating of the eggs.

But thats semantics. Perhaps spongecake is more recognised as the umbrella term.