What is the long tail?
Here is the long tail theory we owe to Chris Anderson in 2004 in the article "The Long Tail" published in Wired magazine.
Roughly speaking, he announced in this article that for some industries and technologies, the turnover generated by the "best sellers" was lower than the turnover generated by all the products infrequently sold.
Applied to SEO, the long tail could be summarized as follows:
If we add on one hand the number of visits generated by all the rarely searched keywords, if we add on the other hand the number of visits generated by the keywords that generate the most traffic and if we compare these two results, we could often realize that the sum of traffic of the unpopular queries exceeds the sum of traffic generated by the most popular queries.
The idea of all of this is that a SEO strategy based only on the most popular keywords is not necessarily the most interesting one.
Let's take a look at some figures that may support this theory: Every day,between 5% and 15% of searches made on Google are searches than have never been made before. And this will increase drastically with the voice search generating so many variations.