History of that day
On that day of 21 February 1952, corresponding to 8 Falgun 1359 in the Bangla calendar, a number of students campaigning for the recognition of Bangla as one of the state languages of Pakistan were killed when police fired upon them.
Mohammed Ali Jinnah(the Governor general of Pakistan) declared that the Urdu will be the only language for both west and east Pakistan at a public meeting on 1948, 21 March. The people of the East Pakistan (now Bangladesh, whose main language is Bengali) started to protest against this.
A student meeting on 21 February called for a province-wide strike. But the government invoked Section 144 on 20 February. The student community at a meeting on the morning of 21 February agreed to continue with their protest but not to break the law of Section 144. Even then the police opened fire and killed the student.
My Salute to all the Martyrs. May their souls rest in peace.