The word has been flattened into a folk theory of cosmic punishment. Its more interesting meaning is closer to: action, understood together with the state it came from.
Karma literally means action or deed. Across Indian philosophical traditions it names the principle that actions have consequences which shape the actor as well as the world — a moral continuity between what one does and what one becomes. Traditions differ substantially on the mechanism, and this book takes no position on the metaphysics.
What it does take a position on is this: the morally decisive part of an action is often not the visible part. Two people can perform an identical act — a donation, an apology, a piece of help — and one of them is building something while the other is buying something. The behaviour is the same. The intention is not.
In Kaliyuga conditions, as described here, people help in order to be seen helping, speak in order to be seen speaking, and act in order to be accepted. None of this is villainy. It is the natural behaviour of a system that rewards the appearance of virtue faster and more reliably than virtue itself. But it hollows out action from inside, and eventually the actor cannot tell the difference either.