The Long Tail refers to the statistical phenomenon that represents the ‘trivial many’ of the Pareto Principle or ’80:20 Rule’ (see the “95:5 Rule“).
Businesses operating in the physical world need to concentrate resources on the ‘important few’, ie the top 20% or even the top 5% that provide the bulk of sales or profits – at the expense of the rest: the ‘trivial many’.
So for example a bookshop can only stock a small percentage of books available in print at any one time and naturally the bookseller will choose the bestselling 5% or less because these will produce the maximum sales. In contrast, the slower selling titles cannot be stocked because they cannot justify the expense of shelf-space.
However in the digital world, shelf space is not an issue. An MP3 music download service can just as easily stock every title, even those ‘trivial many’ that only sell once or twice in a year. In a record shop, stocking these items would be commercial suicide. In the digital world there is virtually no cost to stocking these too, and so even one or two sales are welcome.
The Long Tail refers to the sum total of these ‘trivial many’ items, which collectively can account for more sales than the ‘important few’.
In other words, in the digital world, the ‘trivial many’ can become the ‘important many’.
For more information about the Long Tail, see Chris Anderson’s book of the same name.
Update: Here’s an interesting article by Hannah McNamee about the Long Tail.