Tulsi or Tulasi (Ocimum tenuiflorum) or Holy basil is a sacred plant in Hindu belief. Hindus regard it as an earthly manifestation of the goddess Tulsi, a consort of the god Vishnu. The offering of its leaves is mandatory in ritualistic worship of Vishnu and his forms like Krishna and Vithoba.

Many Hindus have tulsi plants growing in front of or near their home, often in special pots or special small masonry structures. Traditionally, Tulsi is planted in the center of the central courtyard of Hindu houses.

The plant is cultivated for religious and medicinal purposes, and for its essential oil. It is widely known across the Indian Subcontinent as a medicinal plant and a herbal tea, commonly used in Ayurveda.

Source: http://en.wikipedia.org/wiki/Tulsi_in_Hinduism