Aromaticity is a chemical properly in which a conjugated ring of unsaturated bonds, lone pairs or empty orbitals exhibit a stabilization stronger than would be expected by the stabilization of conjugation alone. It can also be considered a manifestation of cyclic delocalization and of resonance. An aromatic compound contains a set of covalently bound atoms with specific characteristics.

(i) A delocalized conjugated system, most commonly an arrangement of alternating single and double bond. 

(ii) Coplanar structure with all the contributing atoms in the same plane.

(iii) Contributing atoms arranged in one or more rings. 

(iv) A number of $\mathrm{\pi }$ delocalized electrons that is even, but not a multiple of 4. This is known as Huckel’s rule. Permissible number of $\mathrm{\pi }$ electrons include 2, 6, 10, 14 and so on.

(v) Special reactivity in organic reactions such as electrophilic aromatic substitution and nucleophilic aromatic substitution. Whereas benzene is aromatic, cyclobutadiene is not. Aromatic compounds typical display enhanced chemical stability as compare to similar non-aromatic molecules.