Graphene

Graphene is a one-atom-thick planar sheet of sp2-bonded carbon atoms that are densely packed in a honeycomb crystal lattice. It is the strongest known material. It can be viewed as an atomic-scale chicken wire made of carbon atoms and their bonds. The name comes from GRAPHITE + -ENE; graphite itself consists of many graphene sheets stacked together.

The carbon-carbon bond length in graphene is approximately 0.142 nm. Graphene is the basic structural element of all materials including graphite, carbon nanotubes and fullerenes. It can also be considered as an infinitely large aromatic molecule, the limiting case of the family of flat polycyclic aromatic hydrocarbons called graphenes.

Source:
Wikipedia. Graphene

Graphene is a single sheet of trigonally bonded (sp2) carbon atoms in a hexagonal structure.

Source:
BSI. PAS 136:2007. Terminology for nanomaterials