Species of the form $\ce{RO^{+}}$, e.g. $\ce{CH3O^{+}}$ methoxylium, $\ce{HO^{+}}$ hydroxylium.
Source: PAC, 1995,
67, 1307. (
Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)) on page 1355 [
Terms] [
Paper]