What is Google Cache?
When we talk about 'cache', we are referring to a type of temporary memory that uses previously processed data to provide the user with quick access to the web page. The data is processed in the background so that it does not need to be reloaded each time it is accessed.
Google's crawlers continually update search results according to new content on web pages in order to provide consistently relevant results: to do this, it needs to 'snapshot' the situation of the pages in question and keep an archive of them.
In case a page cannot be accessed (e.g. for technical reasons), Google will use the latest available snapshot to show it to the user anyway.