Compounds having two acyl groups substituted on ammonia or a primary amine acyl-NR-acyl. They are also known as secondary amides and, especially the cyclic examples derived from diacids, as imides, e.g.
[RC(=O)]2NR,
RS(=O)2NHC(=O)R.
Source:
PAC, 1995, 67, 1307. 'Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)' on page 1331 (https://doi.org/10.1351/pac199567081307)