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 (https://doi.org/10.1515/pac-2018-1010)