[Note: I've updated my About page, which is where I've got the most concise definition of The Long Tail. This post is just a cleaned-up and easily linkable version of that.]

The theory of the Long Tail is that our culture and economy is increasingly shifting away from a focus on a relatively small number of "hits" (mainstream products and markets) at the head of the demand curve and toward a huge number of niches in the tail. As the costs of production and distribution fall, especially online, there is now less need to lump products and consumers into one-size-fits-all containers. In an era without the constraints of physical shelf space and other bottlenecks of distribution, narrowly-target goods and services can be as economically attractive as mainstream fare.

One example of this is the theory's prediction that demand for products not available in traditional bricks and mortar stores is potentially as big as for those that are. But the same is true for video not available on broadcast TV on any given day, and songs not played on radio. In other words, the potential aggregate size of the many small markets in goods that don't individually sell well enough for traditional retail and broadcast distribution may rival that of the existing large market in goods that do cross that economic bar.



The term refers specifically to the yellow part of the sales chart above, which shows a standard demand curve that could apply to any industry, from entertainment to hard goods. The red part of the curve is the hits, which have dominated our markets and culture for most of the last century. The yellow part is the non-hits, or niches, which is where the new growth is coming from now and in the future.

Traditional retail economics dictate that stores only stock the likely hits, because shelf space is expensive. But online retailers (from Amazon to iTunes) can stock virtually everything, and the number of available niche products outnumber the hits by several orders of magnitude. Those millions of niches are the Long Tail, which had been largely neglected until recently in favor of the Short Head of hits.

When consumers are offered infinite choice, the true shape of demand is revealed. And it turns out to be less hit-centric than we thought. People gravitate towards niches because they satisfy narrow interests better, and in one aspect of our life or another we all have some narrow interest (whether we think of it that way or not).

Our research project has attempted to quantify the Long Tail in three ways, comparing data from online and offline retailers in music, movies, and books.

What's the size of the Long Tail (defined as inventory typically not available offline? How does the availability of so many niche products change the shape of demand? Does it shift it away from hits? What tools and techniques drive that shift, and which are most effective?

The Long Tail article (and the forthcoming book) is about the big-picture consequence of this: how our economy and culture is shifting from mass markets to million of niches. It chronicles the effect of the technologies that have made it easier for consumers to find and buy niche products, thanks to the "infinite shelf-space effect"--the new distribution mechanisms, from digital downloading to peer-to-peer markets, that break through the bottlenecks of broadcast and traditional bricks and mortar retail.

The Wikipedia entry on the Long Tail does an excellent job of expanding on this.