graphene

https://doi.org/10.1351/goldbook.08172
Allotrope of carbon, whose structure is a one-atom-thick planar sheet of \(\ce{sp^{2}{-}bonded}\) carbon atoms in a honeycomb (hexagonal) crystal lattice.
Source:
PAC, 2022, 94, 353. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 2021)) on page 426 [Terms] [Paper]