Magento registry is used to share information anywhere in the Magento store. It works like a Global variable. there are 3 static methods (i) register (ii) registry (iii) unregister of the Mage class.
(i) Mage::register:- It is used to register the value in the registry.
(ii) Mage::registry:- (ii) It is used to get the value from the registry.
(iii) Mage::unregister:- (ii) this method is used to remove it from the registry.