What is caching? From Wikipedia: "A web cache is a mechanism for the temporary storage (caching) of web documents, such as HTML pages and images, to reduce bandwidth usage, server load, and perceived lag."
Caching is often thought of as a page-speed ingredient but there is much more to caching than just speedy web pages. Before getting into that, let's briefly discuss three types of caches over which you have some control:
- Browser caching - Your web browser can store web pages, images and other files and server those elements from your computer when you revisit a website. As a webmaster you have some control over how your visitors' browser caches your website.
- Local caching - Some web servers and web sites create a local cache that can store pages from dynamic websites such as those built from WordPress or other content management systems.
- Content delivery network - A CDN stores copies of web site content at various locations around the Internet. Retrieval of that content from the CDN reduced load and bandwidth for your website and is usually results in faster page loads for your visitors.
Why cache?
By caching, you make your footprint smaller, saving server resources including RAM, CPU and bandwidth.
So? you say.
A smaller footprint saves you money. If you need fewer resources, all things being equal your your web hosting cost will also be reduced.
As a bonus, a smaller footprint also happens to give you a faster website. Caching can reduce perceived lag on the site and can reduce the time it takes for a web page to display. We all know what Google has to say about speed -- faster pages is a factor in page rank (PR). Cached pages are [almost] always faster than non-cached pages.
Find out about your caching options in the Webmaster FAQ.