Limonene is the second most abundant terpene in all cannabis strains, but not all strains necessarily have it. As its name says, limonene gives strains a citrusy smell that resembles lemons, which is no surprise as all citrus fruits contain large amounts of this compound. Limonene is used in cosmetics and also in cleaning products. For therapeutic purposes, limonene is known to improve mood and reduce stress. Researchers also found it to have antifungal and antibacterial properties and one research even found it to have a role in reducing tumor size.
Merriam-Webster Online Dictionary
limonene (noun)a widely distributed terpene hydrocarbon CH that occurs in essential oils (as of oranges or lemons) and has a lemon odor - 10 16
Citrus terpene, D-limonene, L-limonene, Dipentene, Carvene