What is cache invalidation?
Cache invalidation refers to process during which web cache proxies declare cached content as invalid, meaning it will not longer be served as the most current piece of content when it is requested.
Several invalidation methods are possible, including purging, refreshing and banning.
The ultimate purpose, of course, is to ensure that the next time a client requests the affected content, the client receives the newest version at all times.
Varnish Enhanced Cache Invalidation is a module within Varnish that enables invalidation of your web content in real-time based on parameters, policies and rules you set to meet your business needs.