Are acids and bases always aqueous?
There are varying definitions of"acid" (or "base") depending on solvent system; some do not involve water at all. For example, there are Brønsted–Lowry acids (proton donors) and Lewis acids (electron acceptors), though the Arrhenius definition is based on aqueous solutions dissociating into $\ce{H+}$ (acid) or $\ce{OH-}$ (base) ions. 

Of course, many acids are not liquids, such as solid citric acid, which may be anhydrous or the monohdrate.