Hydrocarbons (and by extension, derivatives formed by substitution) having two double bonds from one carbon atom to two others
R2C=C=CR2. (The simplest member, propadiene, is known as allene).
PAC, 1995, 67, 1307
(Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995))
on page 1314
Transformed and rewritten from PDF version (entry
http://www.iupac.org/goldbook/A00238.pdf)
by: Miloslav Nic, Jiri Jirat, Bedrich Kosata, ICT Prague, Czech Republic