Science : Known and usually recorded facts and experimentally testable rational explanations thereof.
This also covers mathematics in so far as the theorems of mathematics concern mathematical facts, if only about the properties of certain kinds of imaginary structures. The explanations of mathematics are its proofs (and eventual explanations thereof).
The reason to insist that these facts and their explanations be recorded (if only memorized) is that if they are not they can hardly be shared and made the subject of critical investigation and testing: Science is a fundamentally public affair, conducted by a public of like-minded informed persons.
And science, or scientific knowledge, is special and important in that it is the only kind of human belief that is based on the desire to find the truth about parts or all of reality by logical reasoning and experimental testing of hypotheses.