A theory is, in science, something that is testable and can be disproven, but has as of yet not been disproved and has had all evidence point toward it. The Theory of Evolution is widely accepted by many scientists but is at this point still able to be disproved if someone finds a modern human skeleton from 12 billion years ago. If that were to happen Evolution would be blown out of the water and all the evidence would either be worthless or mean something completely different.