Basses are the lowest singing range. It can be from C2 (lowest) to the A above middle C (highest extreme.) Most basses sing between E2 and E4. Baritone singers generally range between F2-F4, so ApolloFC is correct, the difference is, technically, within two notes. However, you'll find Bass singers usually have a different tonal quality to their vocals than Baritones.
Bass singer:
Boris Christoff as Mephistopheles
Baritone singer:
Simon Keenlyside as Papageno
Obviously, these are opera singers, but I think each singer demonstrates well the difference between the two.