A branch or path or yoga. It is the path of selfless service by performing actions without wanting reward or payment. The principle of Karma Yoga is that what we experience today is created by our actions in the past. Therefore, all of our present efforts become a way to consciously create a future that frees us from being bound by negativity and selfishness.
The yoga of selfless action; yoga through the selfless performance of duties. –Vedanta. (1b) See: yoga. (Du) The yoga (path) of action. (N4)
Path of selfless service, teaching of Krishna in the Bhagavad Gita.