Karma is the law of moral causation.
“If anyone says that a man or woman must reap in this life according to his present deeds, in that case there is no religious life, nor is an opportunity afforded for the entire extinction of sorrow. But if anyone says that what a man or woman reaps in this and future lives accords with his or her deeds present and past, in that case there is a religious life, and an opportunity is afforded for the entire extinction of a sorrow.” – Anguttara Nikaya