spiro compounds

https://doi.org/10.1351/goldbook.S05881
Compounds having one atom (usually a quaternary carbon) as the only common member of two rings, e.g.
S05881.png
Source:
PAC, 1995, 67, 1307. (Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)) on page 1366 [Terms] [Paper]