cp violation is the way that nature breaks the laws that say that when you change a system by c symmetry or p symmetry then some descriptions of the system should stay the same before and after the change. the 'violation' is that they don't stay the same and the amounts are not conserved. cp symmetry says that the laws of physics should act the same on a particle and on its antiparticle (charge conjugation symmetry) and if it was also turned around like in a mirror (p symmetry.)