The generally accepted criteria include (I) one or more homoconjugative interactions (through-space or through-bond); (II) electron delocalization due to effective overlap of orbitals; (III) delocalization of (4n + 2) -electrons in a partially cyclic structure; (IV) bond length equalization of single and/or double bonds; (V) magnetic characteristics associated with "normal aromaticity" and (VI) resonance stabilization energy.