It is the displacement of the electronic pairs π (pi) from the double bonds of the aromatic ring, exerting an equal effect on all regions of the structure. The resonance effect gives stability to the molecule.
This offset is represented by a circle in the center of the ring. Each ring has three π (pi) bonds.
The length of the double bond is shorter than the single bond.
C = C is equivalent to 1.40Å
C - C is equivalent to 1.54Å
Angstron (Å) is a unit of measurement ten billion times smaller than the meter, used to measure bond lengths of atoms, molecules, etc.
We call the aromatic ring containing the resonance resonant hybrid or resonant hybrid.
The way in which the aromatic ring structure is assembled is a canonical form. The canonical forms of the aromatic ring are theoretical. In practice, they do not exist. What exists is an intermediate form between them, which are resonant hybrids.