What is an axiom schema? ZFC is not finitely axiomatizable. But it is, (and I know this is not precise yet) finitely axiom-schematizable. So my question is, what exactly is an axiom schema of a logical calculus like first order logic or propositional logic, such as ((A AND B) IMPLIES B)? Well, I guess it would be a set of statements. But what exactly makes a set of statements schematic?

"Schema" is not a precise term but the well-meaning intent is that it should be easy to enumerate the axioms and it should be easy to decide if a particular formula is an axiom or not.  For example we typically want to be able to verify proofs in polynomial time, so we should demand the same of any "axiom schema".
