Long Tail: "Long tail" is a term typically used to describe an increasingly common retail strategy. First used in this context by Chris Anderson, a writer for Wired magazine, long tail sales involve selling a large number of unique items through small quantities of said product. One famous practitioner of this strategy is Apple, Inc., which sells highly sought-after products, like iPhones, to a significant number of consumers in small quantities; after all, few people are likely to buy two smartphones. Before it's use as a retail term, a long tail was known as a type of frequency distribution in statistics, in which the portion of the distribution has a large number of occurrences which are placed far from the "head", or central part of the distribution. As a result, it has frequently been used as a term in finance and insurance.
A key component of long tail sales, however, describes how for any category of product being sold, there is more aggregate demand for the non-hit, or less common, items than there are for the hit items. Returning to the Apple example, because the company is the only retailer that produces and sells iPhones, they are able to successfully base their business model on the product. In search engine optimization, this concept is the basis behind including long tail keywords in marketing campaigns.