What is judicial activism

In simple terms it means the activism shown by judiciary in resolving cases. Initially, only people who have been aggrieved or hurt or cheated can approach the court. But this restricted entry of people who are not educated or donot have enough finances. So the judiciary introduced PIL(public interest litigation) where anybody from the public can file the case of behalf of people who are being cheated or aggrieved.
And also judiciary has started picking up cases on its own from newspaper or media when it sees that executive is not doing its work. For example: recently supreme court scolded executive for allowing food being wasted in godowns and ordered to distribute it for free. So judiciary is also forcing executive accountability.
In simple terms it means judiciary becoming active and picking up cases on its own  or with the help of public, media to bring justice. And this can be achieved through PIL or SAL(social action litigation). PIL emerged in 1979. And around the same time supreme court took up the case of rights of prisoners. And with this large number of public spirited citizens and voluntary organisations sought judicial intervention for the betterment of life conditions of poor, protection of environment and many other issues.