A hidden form field is a type of input field in a web form that is not visible to the user. It is used to store information that is necessary for the form to function, but does not need to be seen or edited by the user. This hidden field is typically used to pass data between different pages or to store session information. It is hidden from view to prevent users from accidentally altering or deleting the data, ensuring the form functions correctly. Hidden form fields are commonly used in e-commerce websites to store product IDs or in online surveys to track responses. They provide a seamless and efficient way to collect and transfer data without disrupting the user experience.