The word Bihu is derived from the language of the Dimasa people who have been agrarian since time immemorial. Their supreme god is Brai Shibrai or Father Shibrai. The First crops of the season are offered to Brai Shibrai while wishing for peace and prosperity. So Bi means "to ask" and Shu means "peace and prosperity" in the world. Hence the word BISHU gradually became Bihu to accommodate linguistic preferences.The other suggestion is that "Bi" means "to ask" and "Hu" means "to give" and so came BIHU. [[1]] It was said by "Kalaguru" Bishnu Prasad Rabha. In Assam, Rongali Bihu draws from many different traditions— Austro-Asiatic, Sino-Burmese and Indo-Aryan—and is celebrated with great fervor. Celebrations begin in the middle of April and generally continue for a month. This is the traditional new year. In addition there are two other Bihus: Kongali Bihu in October (associated with the September equinox) and Bhogali Bihu in January (associated with the January solstice). Like most other Indian festivals, Bihu (all three) is associated with farming; as the traditional Assamese society is predominantly agricultural. In fact, similar festivals are also celebrated around the same time elsewhere in India.
The three Bihus
In a year there are three Bihu festivals in Assam - in the months of Bohaag (Baisakh, the middle of April), Maagh (the middle of January), and Kaati (Kartik, the middle of October). The Bihus have been celebrated in Assam since ancient times. Each Bihu coincides with a distinctive phase in the farming calendar. The most important and colourful of the three Bihu festival is the Spring festival "Bohag Bihu" or Rongali Bihu celebrated in the middle of April. This is also the beginning of the agricultural season.Bihu is celebrated by the all parts of Assam and all cast and religion.Directly we can say that Bihu is secular festival which brings the humanity,peace and brotherhood among the various cast and religion
Bohag Bihu
Bohag Bihu (mid-April, also called Rongali Bihu), the most popular Bihu celebrates the onset of the Assamese New Year (around April 14–15) and the coming of Spring. This marks the first day of the Hindu solar calendar and is also observed in Mithila,Bengal, Manipur, Nepal, Orissa, Punjab, Kerala and Tamil Nadu though called by different names. It's a time of merriment and feasting and continues, in general, for seven days.