Karma Yoga is defined as  perfection in action; action performed with meditative awareness; the yogic path of selfless service; or, as it's often expressed, work without thought of reward or considering the fruits of one's actions.  It's one of the four yoga paths described in  the Bhagavad Gita (approx. 500 BCE), an allegorical dialogue between Arjuna, the seeker of truth (aka us) and Krishna, the Lord.  Down the millenia echoes the controversy as to whether it is better to retreat into silence and meditation or to stay and act in the world.  The Gita says it's not either/or, it's both.  Arjuna, a warrior, had quailed and become depressed, refusing to fight because it involved killing family members.  Krishna points out that

"He who shirks action does not attain freedom, nor does he gain perfection by abstaining from work.......But they excel who control their senses through their mind and use them...