The product formed by the attachment of an electrophilic or nucleophilic entering group or of a radical to a ring carbon of an aromatic species so that a new σ-bond is formed and the original conjugation is disrupted. (This has generally been called a 'σ-complex', but adduct is more appropriate than complex according to the definitions given.) The term may also be used for analogous adducts to unsaturated (and conjugated) systems in general.
See also: Meisenheimer adduct
PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1170 (https://doi.org/10.1351/pac199466051077)