The ‘cache’ holds copies of recently accessed information such as a web pages and pictures on web pages. It keeps this data on your computer. When you return to the same web page, rather than going to a distant web server to download the original information again, the cache simply serves up the latest copy from your own computer.
Sometimes you are asked to ‘clear your cache’ to remove temporary internet pages so that you view a fresh version of a website rather than possibly stale information.