When we define the aromaticity of a compound, is it meant to describe the resonance hybrid of the compound, or for individual resonance structures of the compound?
I think the latter is wrong because in resonance structures all bonds are localized so there is no delocalisation of electrons, hence we cannot call it aromatic or non-aromatic. Also, resonance structures are hypothetical; they don't exist, so it doesn't seems reasonable to classify them as aromatic, non-aromatic, or anti-aromatic.
Yet, it's common to see some facts rationalised along the lines of "this resonance structure is aromatic and hence has a greater contribution in the hybrid". (For example, Is the aromaticity broken in some resonance structures of para-nitro-aminobenzene? where @ron begins his answer with the line some of the resonance structures in your figure are not aromatic. ) Is this usage of the term 'aromatic' correct / well-defined?