hydrocarbons (and by extension, derivatives formed by substitution) having three or more cumulative double bonds, e.g.
R2C=C=C=CR2.
See also: allenes, heterocumulenes
Source:
PAC, 1995, 67, 1307. 'Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)' on page 1329 (https://doi.org/10.1351/pac199567081307)