In a sort half-joking manner, Cloud computing essentially means, "someone else's computer." It's a half-joke because it's also actually true. When you're consuming Cloud computing resources, which we cover below, you're using someone else's hardware to achieve your goals.
We covered hardware very early on in this book. Imagine that same hardware sitting on your desk, or underneath it, running some software for you (a process and some threads.) Cloud computing is partly about running that same software - the process and the threads - but on hardware that's in a remote location and controled by an organisation. But that alone isn't "Cloud computing" - that's just remote execution.
Cloud computing as a complete picture is the remote hardware and the billing and security models.
These are Cloud agnostic principles that we'll talk about next.