Phytoncide is a term with a broad scope that pertains to any substance that imparts resistance by inhibiting the growth of invading organisms. It was initially introduced by B. Tokin, a Russian researcher, in 1942, in his publication “Bacteriocides of plant origin (phytoncides),” which described plant antibacterial substances. Later on, other Russian scientists broadened the definition to encompass plant-derived substances that exhibit activity against a range of organisms, including both animal and plant pathogens. Phytoncides, as defined, include phytoalexins, pre-existing and post-infectional agents that bestow resistance to plant pathogens, and compounds that repel or eradicate insect pests.