Compounds composed solely of an even number of carbon atoms, which form a cage
-like fused-ring polycyclic system
with twelve five-membered rings and the rest six-membered rings. The archetypal example is fullerene, where the atoms and bonds delineate a truncated icosahedron. The term has been broadened to include any closed cage
structure consisting entirely of three-coordinate carbon atoms.
PAC, 1995, 67, 1307
(Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995))
on page 1336
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. doi:10.1351/goldbook