What is “The Cloud”? What do I say when people ask if my web service is “on the cloud”? [duplicate]

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What is “the Cloud” and how does it relate to development?

First some context: I don't understand what people are asking when they ask "It it on the cloud?" Here is an example. I make a "website" with php that is two pages hosted on a dedicated linux box running apache. One has a form where you upload a file, and the second computes some stuff based on that file and coughs back an answer. Presumably you could call this an API as well if there is a check-box on the form to specify the response as human readable vs. XML. Is that "service" "on the cloud" or it is just a hosted service?

Is gmail "on the cloud"?

Is amazons S3 cloud "on the cloud" or is it "the cloud" or just "a cloud"?

I'm pretty sure at this point that "on the cloud" is marketing jargon for "on the internet" Is there more to it than this? Should I ask this one on english.stackexchange?

To differentiate my question from What is "the Cloud" and how does it relate to development? I am asking specifically how to answer the question I keep getting asked "Is it on the cloud?" without saying "What you are asking is meaningless." given the example of my little web service/API. Is every webpage "on the cloud"?