Karma means action, and just as much the consequence action carries. Every intentional act leaves a trace, and those traces shape what comes next. Not reward or punishment handed down from outside, but the plain physics of a life: the way a habit deepens a little each time it runs.
In yoga the idea is already woven through two concepts beside this one. A samskara is the groove a past action leaves; karma is the law that carries those grooves forward. And the kleshas are its root: Patanjali says plainly that the storehouse of karma is rooted in the afflictions (Yoga Sutra 2.12). Quiet the afflictions and you stop feeding the store.
So karma is not fate. It is the part of the future you are writing now, in how you act. It is also why the path begins with the Yamas: ethics here is not a moral test but a kind of karmic hygiene, cleaner action leaving cleaner traces.
Held honestly. Buddhism carries karma too, and means much the same by it (intentional action and its fruit), but without a permanent self to own it. Where yoga has a Purusha the traces gather around, Buddhism describes the same continuity as interbeing and no-self: the stream of consequence flows on, with no fixed one carrying it. Same mechanism, a real difference in who, if anyone, is reborn.