Ibn Hajar said in ‘Fath al-Bari’ (4/323-324): “There are various explanations of the meaning of the qadr that this night is ascribed to.
It was said that it means veneration, as in the verse: {“...and they didn’t venerate (qadar) Allah as He deserved...”} [al-An’am; 91] This refers to it being a night of veneration due to the revelation of the Qur’an taking place in it, or due to the descent of the Angels in it, or due to the blessing and mercy and forgiveness that descend in it, or that those who stay up that night in worship are venerated.
It was also said that qadr here means constriction, as in the verse: {“...and who is constricted (qadara) in his provision...”} [at-Talaq; 7] This refers to it being a night of constriction due to the exact night being hidden, or because the Earth is constricted due to the presence of such a large number of Angels.
It was also said that it is qadar, derived from the word for judgment. This refers to the fact that all the judgments of that year are made on this night...”