Final answer:
When a molecule can be represented by two or more equivalent structures, it is said to have resonance structures, which are a hybrid of all possible Lewis structures.
Step-by-step explanation:
When two or more equivalent dot structures can be written for a given molecule, it is said to have resonance structures. These are also known as contributing structures or resonance contributors. In the case of resonance, while one can draw multiple Lewis structures, the actual structure of the molecule is a hybrid, or average, of these individual resonance structures. This concept is different from that of structural isomers, where molecules with the same molecular formula have different structural formulas and arrangements of atoms. Similarly, geometric isomers have the same placements of covalent bonds but differ in the spatial arrangement of the atoms, especially in the case of carbon-to-carbon double bonds, resulting in cis and trans configurations.