The long tail, for those of you not familiar with the concept, is a working theory that the web allows for much more diversity than the off-line world. For example, an online bookstore doesn't have the real estate constraints of a typical retail store, or an online music store like iTunes could conceivably sell every song ever recorded while a Best Buy store simply can't.

When choice becomes the norm, the popularity curve shifts to the right. The most popular content becomes slightly less popular, but that's made up for with an increase in popularity of the newly accessibly obscure.

How is this reflected in search engine optimization? Dramatically.

Below is a graph showing the popularity of the top-100 search terms to a website over the past 30 days. As you can tell, there are some terms that drive a tremendous amount of traffic. However, that drops off fairly quickly. While this chart has a tough time showing it, the 100th most popular search term still managed to drive 13 visitors to the site over the course of the month:

What's missing from this graph? The remaining parts of the long tail.

How much further would this graph extend to the right if it displayed every search term that generated traffic for the site over the past 30 days?

Care to guess?

Twice as far to the right?

10 times further right?

In this case, the chart would need to extend 40 times further to the right to display every search term that generated traffic.

How does one manage to acquire traffic on such a large number of terms? Have a large amount of content that people find valuable.

I can guarantee you this: if your website only has a handful of pages, you won't see this type of traffic patter. You'll basically cut the legs off your site's long-tail potential.

An even worse situation would be building your site using non-search friendly markup such as Flash. Words search engines can't see don't help generate traffic for your site.

Should you care?

Probably. The biggest reason why is because the far end of the long tail tends to consist of very specific searches. In many cases, this is the type of traffic that converts to sales the best while the left end of the tail - while driving tons of traffic - tends to convert at a lower rate.