What are Client Server Applications ? A more detailed description

Client server applications are very suitable for the current web world. It is very easy to translate modern web applications into a client server model. For example, if you consider the usage of Yahoo mail that you access through your favorite browser, it is also a client server architecture, at multiple levels. If you consider the case of the Yahoo mail, your browser or mobile runs a client software that connects to a program running at the server which renders the web pages; then the web server itself acts as a client to a database running at the server farm which supplies the actual data that is returned back to the server program, from where it is returned to the client running at the browser.
If you consider the technology of the client server architecture, it is also referred to as a 2 tier architecture, with the 2 tiers being the client and the server. This is the most basic form of the client server architecture, and it can be expanded to go upto using multiple levels such as described in the Yahoo mail program explained above. Both the client and server softwares are normally considered as part of the same software, but they can be modified separately and yet the network keeps on working.
The client server model allows the setting up of such networks that can span across multiple locations, with the client software residing in one location, and the server application in another location. The advantage and simplicity of the client server architecture has made it the prominent architecture behind most modern business and non-business applications. In a mark of how important this model is, even the mainframes of the past have now started using a client server model.