Terpenoids are a large and diverse class of organic chemicals derived from the building block isoprene. They are the most abundant class of plant secondary metabolites, making up around 60% of known natural products and contributing to aromas and flavors. Terpenoids are classified based on the number of isoprene units and carbon atoms they contain, with the main classes being monoterpenes, sesquiterpenes, diterpenes, sesterterpenes, and triterpenes. They play important roles in plants for functions like defense, signaling, and pigmentation, and some terpenoids are precursors for steroids and sterols in animals.