Karma is the Sanskrit word for action, including (and really, ultimately,) our thoughts and the effect of thoughts/actions on ourselves — what would be known in psychology as our conditioning.  Everything one experiences, including in the realm of thought, leaves a kind of mark on us (a fact that is now borne out by modern neuroscience) and therefore affects our future thoughts, impulses, and experiences.  We can overcome the negative burden of this conditioning, our karma, by performing selfless action and ultimately by transcending our narrow, private personality so that all conditioning drops away. Karma yoga, the path of selfless action, is one of the four paths to self-realization.   When this is achieved we have broken this chain of causality and are acting in accord with truth without being controlled by our conditioning. This is accomplished through life-long selfless service and the practice of detached action. Gandhi is, of course, the paramount example of such a “karma yogi.”