If you accuse someone of committing a crime but the proof of the wrongdoing isn't yet found, use the verb allege. You might allege that your sister broke a vase, just because no one else was home when you heard the crash.
If you ever watch news programs, you often hear the verb allege. A reporter might say that detectives allege that a certain person, who is now being held without bail, set a fire. This can be confusing: If the person is in jail, then he or she must have set that fire, right? In reality, the person is a suspect, awaiting trial. In our country, people are assumed innocent until proven guilty in a court of law. That's why we used allege until we know for sure.