The Cloud -- where did we get that metaphor?
The answer is pretty simple. Imagine you are a techie working on an Internet project in the late 1990s. You are explaining to a less-technical audience how your application is going to be built. You have a whiteboard, and you draw some simple things as you talk:
"Here is our datacenter in Los Angeles" -- big rectangle -- "and in the meet-me room we have border routers" -- little circles -- "that are connected to seven other networks and our long-haul links to San Jose and Seattle." You start drawing lines and a vague map of the United States.
One of your colleagues interrupts. "As of next Wednesday, it's going to be nine peer networks."
Inspiration strikes. Instead of concentrating on the specifics of where the networks are connected to each other, you draw a big floofy cloud in the middle of the map, and just draw a line connecting your data center to the cloud, and another line connecting on the East Coast -- maybe around Virginia, maybe around Boston or NYC, it's hard to tell -- and then another rectangle for another data center. "Let's not get into specifics, we're growing and everybody else is growing and the important thing is that it's all interconnected pretty well."
The metaphor works, and pretty soon everyone in your company is drawing a cloud to represent all the parts of the Internet that don't need to be described in depth right now. They go to conferences and draw the clouds; everybody likes this and clouds start appearing in white papers, then official documentation, and eventually it's ubiquitous.
Somewhere around 2000, a person asks where a particular server is, and the engineer at the white board says "it's in the cloud", meaning that the actual position is not relevant, as long as it is well-connected. And after that, everything is "in the cloud".