However, even if a theory is very rich and even if it passes many severe tests, it is always possible that it will fail the next test. It could even fail the same test it has passed many times in the past. A necessary consequence of scientific claims being falsifiable is that they are also fallible. This does not mean the theory is infallibly certain. Scientific facts, like scientific theories, are not infallible certainties, either.
Facts are the world's data.
Theories are structures of ideas that explain and interpret facts. We endeavor to make the mesh ever finer and finer. To the uninformed public, facts contrast with theories. Non-scientists commonly use the term 'theory' to refer to a speculation or guess based on limited information or knowledge. However, when we refer to a scientific theory, we are not referring to a speculation or guess, but to a systematic explanation of some range of empirical phenomena.