Joomla uses query parameters in the dispatcher and controller logic to decide what part of the application should be executed. Fot that it parses the URL and extract the GET and POST variables into the JInput object of the application. The parameters can be read out and used everywhere inside the application to make the decisions.

This is how a URL with the http network protocol looks like:

The section in the URL marked as „query“ is the section where the query parameter or GET variables are placed. Every parameter consists of a key=value pair and is separated by a and-sign (&). It is also possible to pass query parameter within the data section of the http header if you are using a POST request. Joomla will recognise and use both the same way.