Google stores a version of the web page so that if any user searches a relevant query the result can be displayed quickly. Then the stored version of the page will be shown. If your webpage is not available due to some server delay, the cached version will be shown to the user.
TheSource: Google’s document on Cache
cache:operator is a search operator that you can use to find the cached version of a page. Google generates a cached version so that users can still access the web page, for example, if the site isn’t available. While the target audience of the Google cache is Search users, it may be also useful for web creators and developers to get an idea how Google might have seen a page when it indexed it.
How to check the cached version of a page
Caching of the website is checked by “cache:example.com”. This is used to see the cache status of the website. Cache status indicates the active participation of crawlers on your website. If the crawler is visiting your website daily and updating its database with updates that occurred on your website, it means your website is being cached frequently.
But if you are updating your website but it is not being shown in the “cache”, it means Google is not prioritizing your new update occurring on your website.
If your website has not been being cached for a long time, it means your work to get a website ranked, is going to waste. For effective Search engine optimization, your website should be kept on cached.
If your website is not cached and a recent update is not being shown there might be some reasons. Please see the article on why your website is not being cached.