The isocyanic acid tautomer,
HN=C=O, of cyanic acid,
HOC≡N and its hydrocarbyl derivatives
RN=C=O.
Source:
PAC, 1995, 67, 1307. 'Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)' on page 1344 (https://doi.org/10.1351/pac199567081307)