https://doi.org/10.1351/goldbook.M03819
A cyclohexadienyl derivative formed as Lewis adduct from a nucleophile (Lewis base) and an aromatic or heteroaromatic compound, also called Jackson–Meisenheimer adducts. In earlier usage the term 'Meisenheimer complex' was restricted to the typical Meisenheimer alkoxide adducts of nitro-substituted aromatic ethers, e.g. 
Analogous cationic adducts, such as: 
considered to be reaction intermediates in electrophilic aromatic substitution reactions, are called 'Wheland intermediates', and sometimes, inappropriately, σ-complexes.
See also: σ-adduct