Condensation products,
R2C=NN=CR2
, of two moles of a carbonyl compound with one mole of hydrazine (this term should not be confused with the ending -azine appearing in Hantzsch-Widman names for some heterocycles).
See also: aldazines, ketazines
Source:
PAC, 1995, 67, 1307. 'Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)' on page 1321 (https://doi.org/10.1351/pac199567081307)