Short answer: a hypothesis is a specific testable explanation or prediction. A scientific theory is a broader explanatory framework supported by many lines of evidence.
In everyday speech, “theory” often means a guess. In science, that is not how the word is usually used. A scientific theory is not a weak idea waiting to become a fact. It is an organised explanation that helps make sense of observations, generate predictions, and connect many findings.
What a hypothesis does
A hypothesis is narrower. It usually proposes a possible answer to a specific question. For example, a researcher might hypothesise that a particular drug will lower blood pressure more than a placebo in a defined group of patients. That hypothesis can be tested with a study.
A good hypothesis should be testable and falsifiable. It should not be so vague that any outcome can be made to fit. The value of a hypothesis is that it gives research a clear target.
What a theory does
A theory explains a wider range of evidence. Germ theory explains how microorganisms can cause disease. Evolutionary theory explains patterns of biological change and common descent. Atomic theory explains the behaviour of matter at a level we cannot directly see with ordinary senses.
Theories can change, but they do not change casually. They are revised when evidence demands it. A powerful theory does more than explain what is already known. It helps researchers ask new questions and predict what should be found next.
The simplest distinction is this: a hypothesis is something you test within a study; a theory is a larger explanatory structure built from many studies. Confusing the two makes scientific claims sound weaker than they are.