Any compound A00121-1.png. In organic chemistry, an unspecified acyl carbene is commonly a carboxylic acyl carbene, A00121-2.png.
Source: PAC, 1995, 67, 1307. (Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)) on page 1311 [Terms] [Paper]