This is a difficult question. Hope this helps alibi noun a claim or piece of evidence that one was elsewhere when an act, typically a criminal one, is alleged to have taken place. So an alibi is the proof that you were not in a location and is generally used in law. Excuse noun a reason or explanation given to justify a fault or offence. So an excuse is just an explanation. It is not necessarily linked to location and does not have to be true. For example Where were you on Monday? I was with my brother the whole day. The alibi would be the brothers testimony that he was not in the location. The excuse would be that he was with his brother

An alibi is used mostly in the legal sense. Did the suspect have a good alibi? Where was he and what was he doing at the time of the crime, this would be considered his alibi. An alibi will explain your whereabouts in the event someone may accuse you of doing something you may not have done. The suspect was with his mother watching a movie when the girl was murdered. Watching a movie with his mother is his alibi. An excuse is used more often for minor things. They can be good excuses or bad excuses and that is usually determined by the person who is not giving the excuse, the receiver. "She could not go to the movies because she didn't finish putting on her make-up." This would be a bad excuse. "He could not go to class because he had to attend a funeral." With the information you've been given, you can judge that this is a good excuse. An excuse is a "reason for not doing something". I hope this helps! :-)

While it's true that alibi has a legal meaning that is "evidence to prove the accused was at another place at the time of the crime", it is also used colloquially to mean "excuse". When used in this way, it doesn't even have to mean "I was somewhere else". Colloquially, it can be used to mean almost any kind of excuse or mitigating factor. Of course, this is a misuse of the word but that kind of thing happens all the time in English.