https://doi.org/10.1351/goldbook.Q05003
Derivatives of ammonium compounds, $\ce{(NH4^{+})Y^{−}}$, in which all four of the hydrogens bonded to nitrogen have been replaced with hydrocarbyl groups.
Note: Compounds having a carbon-nitrogen double bond (i.e. $\ce{R2C=N^{+}R2Y^{−}}$) are more accurately called iminium compounds.
Example: $\ce{[(CH3)4N]^{+}OH^{−}}$, tetramethylammonium hydroxide.
See: onium compounds