hapticity 

https://doi.org/10.1351/goldbook.08174
Topological description for the number of contiguous atoms of a ligand that are bonded to a central metal atom.
Note:
The hapticity is indicated as a superscript following the Greek letter η.
Example:
(CA5HA5)A2Fe (ferrocene)bis(ηA5-cyclopentadienyl)iron, where η5 can be read as eta-five or pentahapto.
Source:
PAC, 2022, 94, 353. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 2021)) on page 429 [Terms] [Paper]