Wikipedia is an online encyclopedia.
OK, maybe this seems obvious. But it may be more helpful to think about it as telling you what Wikipedia is NOT.
It’s not an advertising platform, a personal website, an experiment in anarchy or democracy, a collection of random data, or a search engine.
It’s not a dictionary, a newspaper, a book or instruction manual, or a collection of found documents.
It's an encyclopedia, a place where you can go to find a good summary of what's already known about a topic.