Pahela Boishakh (Bengali: পহেলা বৈশাখ Pôhela Boishakh or পয়লা বৈশাখ Pôela Boishakh) is the first day of the Bangla Calendar. Poila Boishakh is celebrated in a festive manner in both Bangladesh and West Bengal, as well as by Bengali people in Tripura. Hence, Poila Boishakh connects all ethnic Bengalis irrespective of religious and regional differences. In Bangladesh, Poila Boishakh is a national holiday and in West Bengal it is a public holiday. It falls on April 14 or April 15 of the Gregorian calendar depending on the use of the new amended or the old Bangla calendar respectively. In Bangladesh, it is celebrated on April 14 according to the official amended calendar designed by the Bangla Academy.

Poila Boishakh is also known as Nôbobôrsho (নববর্ষ), or Bengali New Year, as it is the first day of the first month of Boishakh in the Bengali calendar. This day is a very festive time for Bengalis.

Source: http://banglapedia.search.com.bd/HT/P_0023.htm

http://en.wikipedia.org/wiki/Pohela_Baishakh