Carbenes having the structure $\ce{RC(=NR)C{:}–R}$. Imidoyl is a shortened but imprecise term for carboximidoyl, $\ce{RC(=NH)\bond{–}}$.
Source: PAC, 1995, 67, 1307. (Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)) on page 1343 [Terms] [Paper]