Sometimes molecules have more than one valid Lewis structure

Which of these two structures of benzene are correct?  You will learn in these sections how some molecules have multiple Lewis structures.  

Resonance occurs when a molecule has two or more possible valid Lewis Structures.  These Lewis structures collectively describe the electronic structure of the molecule. Resonance structures are capable of describing delocalized electrons that cannot be expressed by a single Lewis formula with an integer number of covalent bonds.