what does long tail mean, Long Tail Theory, Silk Road Network Consulting Company Limited

what does long tail mean,  The analysis and selection of long tail keywords are the main services we offer.We have the integrity of the long tail keyword analytical tool and systematic approach,such as the United States collected large amounts of data search engines professional long tail keyword analysis tool Wordtracker, Google Adwords Keyword Tool, Yahoo Overture Keyword Suggestion, Baidu search related proposals, combined with Alibaba, the global resources, and Google Base competitor keyword keyword approach choose the best long tail keyword.