Overview
Holi is a major Hindu festival of colours, love, and spring, celebrated predominantly in the Indian subcontinent. The festival honours the love between the deities Radha and Krishna, and also marks the triumph of good over evil, commemorating the victory of Vishnu in his Narasimha form over Hiranyakashipu.
Originating in the ancient Indian subcontinent, Holi has spread over time to other regions of Asia and parts of the Western world. Beyond its religious associations, the festival welcomes the arrival of spring in India and Nepal, marks the end of winter, and celebrates the blossoming of love. It is also observed as an invocation for a good spring harvest season.
The festival lasts for a night and a day. It begins on the evening of the Purnima (full moon day) in the Hindu calendar month of Phalguna, which generally corresponds to the middle of March in the Gregorian calendar.
References
Adapted from the English Wikipedia article on Holi.