Many WordPress site owners hear about caching without knowing exactly what it is. And they often mix up two different things: site caching and object caching. In this article I explain in simple terms how they work, which problems they solve and when to turn them on.
What site caching means
Site caching, or page caching, stores static versions of your pages. In practice, when a visitor opens a page, the server does not have to rebuild it every time: it delivers the copy that is already prepared. The result is a faster site and a lighter load on the server.
What object caching means
Object caching is more technical: it stores the results of repeated database queries. WordPress constantly generates requests to display dynamic content. Object caching keeps those results in memory, so they do not have to be recalculated every time.
What is the difference
Site caching = caching of whole pages, useful for blogs, brochure sites and landing pages.
Object caching = internal database caching, useful for complex sites such as e-commerce or membership sites.
When to use them
Site caching should always be enabled, unless your hosting already takes care of it. Object caching is recommended when your site has a lot of dynamic data or high traffic. Redis Object Cache and Memcached are among the most common solutions.
Conclusion
Using caching well means better speed, a better user experience and less load on the server. If you are on managed hosting, first check whether caching is already included: you can read more about cache plugins and managed hosting and about conflicts between cache and CDN. For a full analysis, see also the page on WordPress performance and optimisation.