Cloud Apps vs Web Apps

Question

I have 2 questions:
First, what's the difference between a web application and a cloud application? Are there any differences at all? If I'm developing a web application (a site with many interactive features), can I call it a cloud application?
Second, if there's a difference between a cloud and web application, what languages can cloud applications be developed in? Would a scripting language like PHP be useful for that?


Thanks.

UPDATE: I have watched the video in one of the answers, but I am still a little confused. Taking Google Docs as a example, all I see is a user interface that can be created with html and JS, along with a server script, and the data is stored in a database, which is basically the same thing a web application does. Or is it different?
Thanks

Answer 1

Web applications can run on "the cloud". The cloud is basically a collection of dynamic computational resources (cpu, ram, storage etc) that can be used by web applications.

This allows apps running on the cloud to scale well because they are allocated resources dynamically.

You can use public clouds such as Amazon's EC2 - or build your own private clouds.

A web app running on a cloud isn't exactly a "cloud app" - but the app is simply hosted on a cloud.

I find the first half of this video explains it very well (if a little annoying).

Also see this quesiton which has some good answers.

Answer 2

A web application is an just an application deployed on a web server.
The user accesses this application knowing that it is accessing a remote application and this application has a specific purpose.I.e. implements a specific functionality.

When you start talking about the cloud, you have a different concept alltogether.
The idea is that you want to access a service that you have no idea where the service actually is being deployed.
The main benefit is that a company can save resources.
For example a company can have e.g. their own CRM and have to pay money for servers, for IT personel etc. or just access a service in a "cloud" where the company providing the cloud is responsible for the servers etc.

So to answer your question, to build the cloud you use web applications as "modules" to provide the cloud.

But a web application by itself (separate of this context) can not be considered as cloud application (unless it runs as part of the cloud).