Ocimum tenuiflorum, commonly known as holy basil, tulsi or tulasi, is an aromatic perennial plant in the family Lamiaceae. It is native to the Indian subcontinent and widespread as a cultivated plant throughout the Southeast Asian tropics.

Tulsi is cultivated for religious and traditional medicine purposes, and also for its essential oil. It is widely used as a herbal tea, commonly used in Ayurveda, and has a place within the Vaishnava tradition of Hinduism, in which devotees perform worship involving holy basil plants or leaves. Tulsi is one of the best plants for purifying indoor air quality as it absorbs many toxic chemicals like xylene, formaldehyde and benzene.

The variety of Ocimum tenuiflorum used in Thai cuisine is referred to as Thai holy basil  and is the key herb in phat kaphrao, a stir-fry dish; it is not the same as Thai basil, which is a variety of Ocimum basilicum. In Cambodia, it is known as mreah-prov.