Karma and Samsara
Karma is a Sanskrit word whose literal meaning is 'action'. It refers to the law that every action has an equal reaction either immediately or at some point in the future. Good or virtuous actions, actions in harmony with dharma, will have good reactions or responses and bad actions, actions against dharma, will have the opposite effect.
In Hinduism karma operates not only in this lifetime but across lifetimes: the results of an action might only be experienced after the present life in a new life.
Hindus believe that human beings can create good or bad consequences for their actions and might reap the rewards of action in this life, in a future human rebirth or reap the rewards of action in a heavenly or hell realm in which the self is reborn for a period of time.
This process of reincarnation is called samsara, a continuous cycle in which the soul is reborn over and over again according to the law of action and reaction. At death many Hindus believe the soul is carried by a subtle body into a new physical body which can be a human or non-human form (an animal or divine being). The goal of liberation (moksha) is to make us free from this cycle of action and reaction, and from rebirth.