A scientific hypothesis (pl. hypotheses) is an evidence-based, testable, and falsifiable (can be shown to be wrong) statement about how some aspect of the world works.
A hypothesis is usually written in the form of an if/then statement. It could also include the word "may".[1]
A simple example of a hypothesis could be "fire requires oxygen." It is evidence-based because fire is seen to exist in air, which contains oxygen, and can be put out by water which can cut off the air supply to the fire. It is testable because you can devise a test (removing oxygen from the area of a fire) that will either affirm the hypothesis or not. It is falsifiable because if you take away oxygen from a fire, and the fire continues to burn, the hypothesis is shown to be wrong.