What is shab e miraj?

Shab e Miraj means the night of ascent. In which, Prophet Mohammed (PBUH) was invited by Allah (the God) to heaven. "The Buraaq", a extremely swift transport was sent to carry holy prophet (PBUH). at that night, gift of five Salah (prayer) made compulsory for all Muslims.

Source: (termexplained.org/Islam/shab-e-meraj)