First of all you need to know what is Cloud application. See the definition
Quote:
A cloud application (or cloud app) is an application program that functions in the cloud, with some characteristics of a pure desktop app and some characteristics of a pure Web app. A desktop app resides entirely on a single device at the user's location (it doesn't necessarily have to be a desktop computer).
It is the definition from
searchcloudapplications.techtarget.com/definition/cloud-application
So the applications are using such as CodeProject, Facebook, Gmail etc. may or may not be using Cloud platforms for providing the service. As cloud supports different types of services, based e on the application's need the provider can choose which one to choose.
Due to the evolution of Cloud technologies, now-a-days applications which require real-time computations, manipulations are using cloud as the deployment platforms.
At the user end you cannot determine whether the application is cloud based or no unless it has been explicitly mentioned. For example, you have a web site and database server, you can host your site in a server and it runs, people access it and it works ok. With the same functionalities, you can host the site to cloud, to the users there will be no difference as they may be accessing the same url, but in terms of maintainance of the site is totally different as the server and site resides on the cloud.
Hope this will answer your question.
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