The Sanskrit word karma means "actions" or "deeds." As a religious term, karma refers to intentional (usually moral) actions that affect one's fortunes in this life and the next. Karma (or kamma in Pali) is a concept common to Hinduism, Buddhism and Jainism, but interpreted in different ways.
The concept of karma or "law of karma" is the broader principle that all of life is governed by a system of cause and effect, action and reaction, in which one's deeds have corresponding effects on the future. Karma is thus a way of explaining evil and misfortune in the world, even for those who do not appear to deserve it - their misfortune must be due to wrong actions in their previous life.