A query string is a part of a URL (Uniform Resource Locator) that is used to send information to a web server. It usually consists of a series of parameters and values appended to the end of a URL and is used to specify certain actions or retrieve certain information from a server.
For example, consider the following URL:
In this URL, the part after the "?" is the query string. It contains a parameter called "q" and the value "query string". When this URL is called, the web server interprets the query string and performs a search for the specified term ("query string").
Query strings are often used to send data to a server in the form of key-value pairs. They are often used in web applications to pass data between the client (usually a web browser) and the server. They can also be used to send data to a server when a form is submitted or to specify certain actions for the server to perform, such as a search query or sorting data in a certain way.