A resource is a special variable, holding a reference to an external resource. Resources are created and used by special functions. The following is a list of functions which create, use or destroy PHP resources. The function is_resource() can be used to determine if a variable is a resource and get_resource_type() will return the type of resource it is. https://www.php.net/manual/en/resource.php This is a common yet one of the most important PHP coding interview questions and answers for experienced professionals, don't miss this one.