Web Applications refer to the highly advanced website which is connected to a server & consist of server side scripting to connect the web page to a database that stores all the data about the brand & its customers.
It is mostly used by banks, e-commerce & brands with a huge audience, etc.
These applications uses the server to store all the data of the brand website in a very efficient manner where the programmer rents an amount of space from established hosting providers.
These applications use the cloud computing concept to store data in the cloud space that does not consist of a particular server hosting provider.
This refers to the process of design & development of a website that is visible to the client.
This refers to the backend process of connecting the website to the server database which is actually not visible to the client.