Source is a specific type of magically capable person. They have natural abilities allowing them to draw magic more easily or cast spells accidently. Best comparison is that of a musician with a perfect pitch. Being a Source is like having perfect Pitch. Even if you don't have it, you can still learn nearly everything as to how to make music, but when you do have it, everything is much easier. Sourcesare also very rare: in the Games, we meet 2 of them (Alvin and Ciri)
