Noncovalent attractive force between a positive ion (metal cation, protonated Brønsted base, etc.) and a
\(\ce{\uppi\ electron}\) system.
Source:
PAC, 2022, 94, 353. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 2021)' on page 381 (https://doi.org/10.1515/pac-2018-1010)