Event receiver is nothing but a piece of server side code which gets executed whenever the user interacts with the SharePoint components, such as the lists, document libraries, site collection, web application.
SharePoint 2013 introduces a new Event Receiver class named as SPSecurityEventReceiver. Using this class, we can create event receivers for the action, such as the User group creation & deletion, Inheritance changes, Role Definition addition, deletion etc.
The following are the list of the newly added group events in SharePoint 2013.
Inheritance Events
InheritanceBreaking
InheritanceBroken
InheritanceReset
InheritanceResetting
User Events
GroupUserAdded
GroupUserAdding
GroupUserDeleted
GroupUserDeleting
RoleAssignmentAdded
RoleAssignmentAdding
RoleAssignmentDeleted
RoleAssignmentDeleting
RoleDefinitionAdded
RoleDefinitionAdding
RoleDefinitionDeleted
RoleDefinitionDeleting
RoleDefinitionUpdated
RoleDefinitionUpdating
Group Events
GroupAdded
GroupAdding
GroupDeleted
GroupDeleting
GroupUpdated
GroupUpdating