Caching, as it pertains to hosting a website, is the temporary storage of content. This content could be images, files, bits of PHP scripts that are precompiled, HTML pages, results of database queries, and other web objects.
Why Use Caching?
Caching quickens the responsiveness of your website. You’ll also hear this concept referred to as: reducing latency, eliminating redundant processing steps, improving responsiveness, or reducing load times.
How is Caching Used?
Some mechanisms of caching take generally complex requests, such as PHP pages, and make them simple requests, such as static HTML pages. Other mechanisms of caching also store resultant data… examples would include: copies of pre-compiled PHP scripts or results to database queries. And still others, such as a content delivery network (CDN), distribute copies of content to many nodes.
To summarize, caching stores resultant simple content after a complex request, or temporarily stores copies of content in an easily and quickly accessible manner.