A scientifically testable explanation or proposal.
Example: A researcher organizing a psychology study thinks that people who are angered right before completing a task are more likely to finish the task quickly, compared with non-angered people. This is her hypothesis.
Grinnell, R. (2009). Hypothesis. Psych Central. Retrieved on April 22, 2015, from http://psychcentral.com/encyclopedia/2009/hypothesis/