Most Web pages combine content that is static with content that is dynamic.
An example of dynamic content is stock ticker data. The static content will change so infrequently that you know it will always be on the page. An example of static content is a Web site's logo. The content that changes infrequently would be stored in the client's memory cache. The larger number of static items you have on your Web site, the greater the performance increase you can get by caching that content.