Thank you so much..Above link is helpful in my seminar - improve response time and throughput of search engine with web caching.please Give me Practical example on this topic which may be helpful in my seminar.
well if you have visited the above link than you might have got basic idea that in web cacheing your site pages that you think are modified not very frequently are placed on catche web server. A person visiting your site feels that your site is loading fast as copy of some of our site's web pages are present on cache web server.
off course their are issues like security and freshness of pages. But i think for better user experience, compromise can be made.
certainly there are provision to address these issues(which are server side tags not html tags).
so you can say it is better to cache your site on free web servers than to buy and maintain a large no. of web servers arround the world to lower response time for better user experience.
this is even not possible for small organisation to buy and manage web servers. So web caching is best solution for most of us and that is also free!
please refer to above links given by LastMitch for further technical details.