Cations having the structure $\ce{R2C=N^{+}}$. A contraction of alkaniminylium ions. Alkylideneaminylium ions is a synonymous term. A subclass of nitrenium ions.
Source: PAC, 1995, 67, 1307. (Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)) on page 1344 [Terms] [Paper]