Cache: Instead of searching the entire internet whenever a user enters a query, search engines perform what is called search engine indexing, or web indexing. In this process, the search engine collects, parses and stores data, allowing the search engine to quickly and accurately retrieve this information as needed. A cache, therefore, is where a search engine stores copies of a web page from their index to facilitate the searching process.
It is possible to see evidence of this system when you conduct a Google search: the search engine will provide a link that reads "cached" next to each item on the search result page. This link allows the user to access a copied web page from the index, which can prove useful when a web server makes web pages unavailable either temporarily or permanently.
Caches are also used in a variety of other ways to simplify the storage and retrieval of data. For example, web browsers and web proxy servers use caches to reduce the amount of information that must be transmitted to retrieve a web page, which decreases the amount of bandwidth and processing requirements needed. This effectively makes the web server more responsible to user requests.