Hypothesis: Statement or theory that is assumed, possibly tentatively, as an explanation for a given (supposed) fact.
The so-called hypothetico-deductive method of science is a term for the notion that science proceeds by guessing hypotheses by abduction that then are confirmed or infirmed by induction by verifying or falsifying deductive consequences of the hypothesis.
Two properties any hypothesis should have to be counted as a scientific hypothesis are that it is consistent with such knowledge as one assumes one has, and that it logically implies a statement that can be verified or falsified by some experiment. The reasons are that an inconsistent hypothesis deductively implies anything, including its own falsity, and that a hypothesis from which one cannot deduce experimentally testable predictions simply cannot be tested and so must remain pure fiction. Similarly, a hypothesis starts to be scientifically credible only if it has passed some test i.e. some of its predictions have been verified.