Graphene is an allotrope of carbon consisting of a single layer of atoms arranged in a two-dimensional honeycomb nanostructure (an intermediate-sized structure between microscopic and molecular structures).

Allotropy is the phenomenon of the existence of different varieties of the same chemical element in the same state of matter, differing in their physical and chemical properties. Allotropic varieties of an element may differ in their crystal structure or the number of atoms in the molecule.