A concept of cause and effect found in Buddhism, Hinduism, and other Asian religions. The basic idea is that doing good things in the world will influence the world in a positive way and thus bring more positivity into your own life (that is, the life of the person who does the positive things). Likewise with negativity: do negative things, make the world more negative, negative things will happen to you. However, in spoken English it's often used casually to just mean when someone "get's what's coming to them". That is, something bad happens to them right as they were doing something bad. So if someone tries to cheat at a board game and then accidentally gets poked/hurt with a piece from the board game, an English speaker might call it "Karma" or "instant Karma". You can find lots of videos on youtube that illustrate this point better than I can explain it.