Hypothesis
A hypothesis is a proposed explanation for a phenomenon.
In the hypothetico-deductive method, a hypothesis should be falsifiable, meaning that it is possible that it be shown to be false, usually by observation.
As an example, a reader who comes upon a high-quality article in Wikipedia might form a hypothesis that Wikipedia articles can only be edited by highly qualified professors with multiple Ph.Ds.
It can be considered a hypothesis, as it is falsifiable. It can be falsified by noticing that anyone can edit Wikipedia articles, using the "Edit this page" link on all pages, and by remembering that very few people are highly qualified professors with multiple Ph.Ds. An experiment in this regard would be to find someone who is either not a professor and/or has at most only one Ph.D. (e.g. yourself), and request that person to click the "Edit this page" link, edit the page, and save. If the replaced page appears, then the hypothesis is falsified (provided that the experimental uncertainties are small and that the experimenter has correctly interpreted the statement of the hypothesis), and the experiment ends.
See Philosophiae Naturalis Principia Mathematica for Newton's position on hypotheses, "Hypotheses non fingo" : "I feign no hypotheses" [1].
See also Statistical hypothesis testing.
[1] Isaac Newton, Principia Mathematica. A New Translation by I. Bernard Cohen and Anne Whitman, translators. University of California Press 1999 ISBN 0-520-08817-4