Bitcoin is money that no one controls, run by thousands of computers around the world that all keep the same record of who owns what.
That is the whole idea in one sentence. Everything below this point on the map is just an answer to the question "how does that actually work?"
Launched in January 2009 by the pseudonymous Satoshi Nakamoto, Bitcoin was the first widely used system to solve the problem of double spending for digital money without a bank in the middle. Instead of trusting a company, users trust open-source software, mathematics and a set of shared rules.