Buddhism accepts from Hinduism the concept of Karma in order to put a stop to it, via Nirvana as the realization of emptiness. The fact that Karma and Emptiness are at odds was only realized later, and this fact drove a lot of the intellectual development of Buddhism as it tried to resolve this issue. A good place to start when trying to understand this is the Awakening of Faith which explains that there is a kind of consciousness called storehouse consciousness where the seeds of Karma are laid down, and where they persist in order to drive ones destiny later or give continuity to consciousness.
Karma is the persistence of causality across moments of time, or across lives. Basically anything you do that is wrong comes back to haunt you and what ever you do that is good eventually comes back to help you. But this is at odds with the idea that everything is empty. If everything is empty then where does the seeds get their persistent reality, and where can the seeds be put that exists long enough for them to fructify? Karma is seen to be ultimately empty, but that emptiness has to allow for illusions to appear real to ordinary mortals. Buddhism has the doctrine of two truths, and says that both views exist, one that sees illusion as real and one that sees emptiness. But the karma must also be real in some sense because it is what makes the emptiness dynamic so we see the flux of existence.
Ultimately the Heart sutra declares that Form is Emptiness and Emptiness is Form. Karma is the dynamic function that makes it appear as if forms are arising and going out of existence. So we get statements like non-arising and non-ceasing to describe the nature of existence. Eventually this leads to the idea that Emptiness is interpenetration which is the nondual combination of Karma and emptiness which is dynamic flux of aggregates that all reflect each other as Indra’s Jeweled Net.
So if we jump all the way to Hua Yen Buddhism of Fa Tsang then we can say that Karma is the dynamic quasi-causality that operates in spite of emptiness and is what makes emptiness into interpenetration.