Each carbon has one electron in a p-orbital.
Each p-orbital can overlap with the p-orbital on either adjacent carbons.
Thus the π electrons are not localized between two carbon atoms but are delocalized in an electron cloud above and below the ring.
Thus each carbon-carbon bond in benzene is equivalent.
The delocalized electrons can be represented by two structures differing only in electron position
separated by a double-headed arrow.
These structures are referred to as resonance forms. The true structure of benzene (or other species for which such forms can be drawn) is not represented by any of the resonance forms but by a resonance hybrid more stable (less reactive) than any of them.
Some textbooks represent the delocaisation of electrons in benzene by drawing a circle in the middle of the ring.