They are just longer phrases with a more exact intent by a searcher. For instance SEO isn’t a long tail keyword. Ultimate SEO isn’t either but its twice as close to it. Ultimate SEO FAQs is just about there and you can see that its more and more specific… Ultimate SEO FAQs On Long Tail Keywords …. now thats a long tail keyword.
They are searched less but they are much more specific and its easier to rank well for them with the right content.