What is Query String?
A query string is the portion of a URL where data is passed to a web application and/or back-end database. Query string commonly includes fields added to a base URL by a Web browser or other client application, for example as part of an HTML form.
Why We Need Query String?
Since HTTP protocol is stateless, query strings provide a great way to transfer dynamic data between client and server. There are a number of other ways to do this, like session or cookie. But apparently, query string is the most easy and clean way maintain states between client and server.