The term “long tail” refers to a typical graph of probability distribution. In a typical probability distribution, the majority of the items graphed will be in the middle portion, with a the distribution getting thinner and smaller as you move to the right.
When you apply this to SEO, you can see that there are a small number of keywords that are extremely popular, a large group that has middling popularity, and then lots and lots of different keyword phrases that get only a few clicks. The red area of the image, represents the long tail.
What the Long Tail Is NOT
Some people will tell you that a long tail keyword phrase is defined by the length of the phrase. While this may have been true several years ago, it is no longer true. A long tail keyword phrase is a phrase of any length that gets a small amount of search traffic. Long tail keywords were defined by their length because people used to only search for one or two words at a time. But that is no longer true.
A long tail keyword phrase is also not a phrase that generates only one or two results. For example, you can do a search for your own website by putting in the URL of your site. This should generate just your site in the results. But it is so specific that the likelihood that anyone is searching for it other than you is very low. Do research on the phrases you are considering and make sure they are not so specific that they are unhelpful.
