According to what Spekkio says, Magis is the manipulation of the four fundamental forces (magical elements) governing the universe. Of course, there are different ways to go about this. Some living things (Crono, Heckran, Lavos, etc) can somehow directly control the elements with their bodies. The Enlightened Ones in Zeal were given magical powers by the eminations of the Mammon Machine and possibly the Sun Stone. Robots lack the magical ability of living things, but they can produce similar effects through mechanical means.