Rajas is, in the Samkhya philosophy and the Bhagavad Gita, the second of the three gunas, the strand of activity, passion, movement and desire, the quality of energy, restlessness, ambition and craving that drives action and change. In the threefold analysis of nature it is the principle of motion and of the turning of the world, neither revealing like sattva nor concealing like tamas but impelling, the force behind striving, attachment and the ceaseless pursuit of ends.
The Bhagavad Gita characterises rajasic food, action and temperament as those marked by intensity, agitation and the hunger for results, and it identifies rajas as a chief cause of the bondage of the soul to action and its fruits. Yet rajas is necessary, for without it there is no movement at all; the teaching is not to eliminate it but to govern it, favouring the clarity of sattva while recognising that the settled tendency of nature is the interplay of all three. The doctrine is ancient and central to Hindu and yogic thought.
Sources Classical Samkhya: An Interpretation of Its History and MeaningGerald James Larson with Srimad-Bhagavad-Gita, English translation and commentarySwami Swarupananda