Credo is Latin for, literally, "I believe," and originally meant a particular religious belief. Now it has the far broader meaning of any system of principles that guide a person or group.
There's often a faintly jokey air to the word as used today, perhaps in recognition that it once popularly held such a high-minded meaning. A hedonist's credo might be simply "party on," or "enjoy the ride;" an actor's "the show must go on." Politicians have credos, and so too, presumably, do rappers and weather forecasters.