What is the relation between a hypothesis and theory?

A hypothesis is a tentative theory which is unverified, but if true could explain selected facts or observations. A hypothesis expresses an opinion which isn't necessarily based on provable evidence.

A theory is a little more solid than a hypothesis, so a hypothesis when tested and proved to have some basis might become a theory.

A theory might also refer to a belief with little or no fact behind it at all: he has a theory that the month in which people are born affects their personalities.