Quick Definition: A testable explanation for an event
From Rational Wiki:
“Hypothesis” (like the word theory) has a few different meanings – the common usage, a more exact scientific one and also a meaning instatistics, such as null hypothesis. The meanings behind “hypothesis” are rarely confused, except when people try to abuse language for the furtherance of ideology, as in the way creationists use the words “theory” and “hypothesis” to try to delegitimize scientific ideas they do not like. Conflating these is often one of the sources of confusion and criticism of science.
In everyday language, a hypothesis means a possible explanation for a phenomenon. This can be an idea that is merely PIDOOMA in nature, or something that follows common sense. Often, it’s considered a somewhat “weaker” form of the term theory, as if a theory is only a hypothesis that has more support – but this isn’t the case, and the distinction between hypothesis and theory is part of the scientific definitions of the two terms.
In science, the meaning is more precise. As part of the scientific method, a hypothesis is the stage where a testable statement is generated. In this case, a hypothesis is usually an original idea generated from data, or from existing theories, which is tested for its ability to explain and predict phenomena. A successful hypothesis lends support to the theory that produced it, and the successful theory will produce further hypotheses to be tested. For instance, a theory about gravitation would produce a hypothesis about the orbits of planets – the orbit of Mercury being a specific hypothesis that differentiated classical Newtonian mechanics with general relativity as a model for gravity.
There are often a multiplicity of hypotheses on any subject which are slowly (or quickly!) winnowed down to one or two similarly viable possibilities. The ability of an hypothesis to make viable predictionsis used to test its validity. The inability of one to do so tends to make it evident that it is not actually scientific.