<P> Between 2005 and 2010, the number of web users doubled, and was expected to surpass two billion in 2010 . Early studies in 1998 and 1999 estimating the size of the Web using capture / recapture methods showed that much of the web was not indexed by search engines and the Web was much larger than expected . According to a 2001 study, there was a massive number, over 550 billion, of documents on the Web, mostly in the invisible Web, or Deep Web . A 2002 survey of 2,024 million web pages determined that by far the most web content was in the English language: 56.4%; next were pages in German (7.7%), French (5.6%), and Japanese (4.9%). A more recent study, which used web searches in 75 different languages to sample the Web, determined that there were over 11.5 billion web pages in the publicly indexable web as of the end of January 2005 . As of March 2009, the indexable web contains at least 25.21 billion pages . On 25 July 2008, Google software engineers Jesse Alpert and Nissan Hajaj announced that Google Search had discovered one trillion unique URLs . As of May 2009, over 109.5 million domains operated . Of these, 74% were commercial or other domains operating in the generic top - level domain com . Statistics measuring a website's popularity, such as the Alexa Internet rankings, are usually based either on the number of page views or on associated server "hits" (file requests) that it receives . </P> <P> A web cache is a server computer located either on the public Internet, or within an enterprise that stores recently accessed web pages to improve response time for users when the same content is requested within a certain time after the original request . Most web browsers also implement a browser cache by writing recently obtained data to a local data storage device . HTTP requests by a browser may ask only for data that has changed since the last access . Web pages and resources may contain expiration information to control caching to secure sensitive data, such as in online banking, or to facilitate frequently updated sites, such as news media . Even sites with highly dynamic content may permit basic resources to be refreshed only occasionally . Web site designers find it worthwhile to collate resources such as CSS data and JavaScript into a few site - wide files so that they can be cached efficiently . Enterprise firewalls often cache Web resources requested by one user for the benefit of many users . Some search engines store cached content of frequently accessed websites . </P>

What do you understand by world wide web