[4] Plant terpenoids are used for their aromatic qualities and play a role in traditional herbal remedies.
Terpenoids play a role in plant defense as prophylaxis against pathogens and attractants for the predators of herbivores.
[6] Terpenoids are modified terpenes,[7] wherein methyl groups have been moved or removed, or oxygen atoms added.
Just like terpenes, the terpenoids can be classified according to the number of isoprene units that comprise the parent terpene: Terpenoids can also be classified according to the type and number of cyclic structures they contain: linear, acyclic, monocyclic, bicyclic, tricyclic, tetracyclic, pentacyclic, or macrocyclic.
[9] Terpenoids, at least those containing an alcohol functional group, often arise by hydrolysis of carbocationic intermediates produced from geranyl pyrophosphate.