Doctrine of 'Ijtihad in Islamic Law means :

It refers to accept the juristic opinion and verdict of a mujtahid (jurist) and to act upon it.

It refers to the cases in which the total shares of the shares exceed the heritable property, the fractions are reduced to a common denominator.

It means the independent or original interpretation of problems not precisely covered by the Quran.

It refers on the assumptions of a lawful union between the parents of the acknowledged child.