web.config: AppSettings In web.config

 Here is the article.

Please take a look how the introduction is written. 

ASP.NET provides a configuration system we can use to keep our applications flexible at runtime. In this article we will examine some tips and best practices for using the configuration system for the best results.

The <appSettings> element of a web.config file is a place to store connection strings, server names, file paths, and other miscellaneous settings needed by an application to perform work. The items inside appSettings are items that need to be configurable depending upon the environment, for instance, any database connection strings will change as you move your application from a testing and staging server into production.