Moksha that translates into liberation, is the fourth and final goal of the lives in the purushartha sequence. What it is and why is this so important a concept ?
Hinduism puts forward the idea that the cycle of birth-death-rebirth again keeps going on, making the soul accumulate and at the same time undergo the fruits of such previously accumulated karma. It is both heaven and hell that come on the way giving the good and bad fruits. They are not permanent. They are only transient spots and the journey of the soul continues beyond.
Along with the karma there are two culprits – ego and illusion – that make the soul do more deeds and accumulate more and more karma. Put together these impurities are referred as pasha or bondage, as they bind the soul in this never ending vicious circle.
Liberation is when the soul is no longer bound to these impurities and comes out of the cycle and the result is Eternal Bliss. Supreme or parabrahman is the One which stays beyond these cycles and that Supreme is invoked by the soul to come out of the cycle and stay in the Bliss without reincarnating. This is the ultimate state all the bonded souls need to get to !
While the concept of liberation and the soul freed from bondage and staying in Eternal Bliss is the core Hinduism concept shared by all philosophies of it, the philosophies describe the finer details differently like the relation between the soul and the God at the state of liberation etc. Those interested in the analysis of the philosophy and enjoy the wisdom they bring to the seeker can go through in detail about the philosophies like advaita, siddhantha, dvaita etc.
Without getting to the hells, heavens and the worlds, Oh God, you blessed the devotee to get to the Supreme State ! – thiruvasakam