Using someone else's computers over the internet instead of buying and maintaining your own hardware. Like renting a car instead of buying one.
Instead of buying expensive servers, Netflix uses cloud computing to stream videos to millions of people.
Cloud computing is a broad model (not a single service) where you rent computing resources—servers, storage, databases, networking, and software—over the internet. AWS, Azure, Google Cloud, and OCI are cloud providers that offer many services that together enable cloud computing.