Pahela Falgun (Bengali: পহেলা ফাল্গুন Pôhela Falgun or পয়লা ফাল্গুন Pôela Falgun), first day of Spring of Bengali month Falgun, of the Bengali calendar, celebrated in Bangladesh and West Bengal and in the other Indian states, including Assam, Tripura, Jharkhand and Odisha. The first of Falgun usually falls on 13 February of the Gregorian Calendar. This day is marked with colourful celebration and traditionally, women wear yellow saris to celebrate this day. This celebration is known as Bosonto Utsob (Bengali: বসন্ত উৎসব ; Spring Festival).
Pahela Falgun Wikipedia
In Bengali, Pahela stands for 'first' and 'Falgun' is eleventh month of the Bengali calendar.