The term long tail refers to the ability of online providers to offer a very broad and deep product range. This contrasts with stationary sales formats, which have to concentrate on fast-turnaround items due to space constraints and for reasons of profitability.
The term long-tail is derived from the long list of items that can be ordered, stocked and offered at a relatively low cost. Whereas the product selection of a traditional retail store is a few hundred or a few thousand products, the assortment of online providers can consist of several million products. Even if exotic products are only sold in small quantities, these products cannot be marketed via traditional retail outlets for cost reasons.
Examples of online stores are the iTunes Store, which offers millions of different pieces of music for downloading, or Amazon with a very broad and deep range of goods that cannot be reproduced by any stationary department store.