For example, resources are used to store database links and file descriptors.
Resources are a special kind of data type in PHP. The term resources doesn't really refer to any special kind of data, but to an abstraction method for maintaining any kind of information. Resources are kept in a special resource list within Zend. Each entry in the list has a correspondending type definition that denotes the kind of resource to which it refers. Zend then internally manages all references to this resource. Access to a resource is never possible directly - only via a provided API. As soon as all references to a specific resource are lost, a corresponding shutdown function is called.