A hypothesis is a proposed explanation for a phenomenon. In the scientific method, a hypothesis is an educated guess or prediction about how something works. It is based on observations and prior knowledge. A good hypothesis should be testable and specific.
A hypothesis must be tested through experimentation in order to determine if it is correct or not. If the results of the experiment support the hypothesis, then it becomes a theory. If the results of the experiment do not support the hypothesis, then it must be revised or rejected altogether.
There are many different types of hypotheses: null, directional, and non-directional to name a few. Each type has its own strengths and weaknesses that should be considered when designing an experiment.