A querystring is the portion of a dynamic URL that contains search parameters . In a URL, the querystring follows a separating character, usually a question mark (?). Identifying data appears after this separating symbol. The querystring consists of one field or variable (technically called a key), then followed by an equal sign (=), followed by the value for that key. Each key and its corresponding value, donated as the equation, is called a key-value pair. A querystring may contain several key-value pairs. When there is more than one key-value pair, they are typically separated by an ampersand (&).
In the example above, the value for the key includes a codesnippet which is a value field surrounded by double quotes (ex. %%emailaddress%%). When the URL is clicked on, the system will search the database and retrieve the value of the codesnippet and insert the data into the link to prepopulate the form.