It is called Lailatul Qadr For Several Reasons...

A renowned exegetist of the Quran, Mufti Ahmad Yar Khan Alaihir raHmah has stated: This night is called Lailatul Qadr for several reasons:

1. In this night, the tasks of the following years are set and assigned to the angels. Qadr refers to either destiny or dignity.

2. The Holy Quran was revealed at this night.

3. The worship performed in this night has great Qadr (excellence).

4. Qadr also means ‘narrowness.’ Angels descend at this night in such a great number that the earth is crowded with them.

For these reasons, this night is called Lailat al-Qadr. 

[Mawa’iz-e-Na’imiyyah, Page 62]