out of the blue

This is a great definition of Direct Marketing that I found at Wikipedia. Enjoy.
Direct marketing is a sub-discipline of marketing focused on driving purchases that can be attributed to a specific “call-to-action”. Direct marketing is distinguished from other marketing efforts by its emphasis on trackable, measurable results (known as “response” in the industry) regardless of medium.

Direct marketers use a variety of media including catalogs, postcards, statement inserts, card packs, magazines and other mail. Direct marketers also use media such as door hangers, package inserts, magazines, newspapers, radio, television, email, internet banner ads, pay-per-click ads, billboards, transit ads, etc. If the ad in the medium asks the prospect to take a specific action–call an 800 number, visit a website, return a response card, place an order, complete a survey, etc.–then the effort is considered to be direct marketing.

The term is believed to have been first used in 1961 in a speech by Lester Wunderman, who pioneered direct marketing techniques with brands such as American Express and Columbia Records. Although Wunderman may have been the first to use the term “direct marketing”, the practice of “mail order selling” (direct marketing via mail) essentially began in the U.S. upon invention of the typewriter in 1867. The first mail-order catalog was produced by Aaron Montgomery Ward in 1872. The Direct Mail Advertising Association, predecessor of the present-day Direct Marketing Association, was first established in 1917. Third class bulk mail postage rates were established in 1928.

Direct marketing’s history in Europe can be traced to the 15th century. Upon Gutenberg’s invention of moveable type, the first trade catalogs from printer-publishers appeared sometime around 1450.

Direct marketing is attractive to many marketers, because in many cases its effectiveness can be measured directly. For example, if a marketer sends out one million solicitations by mail, and ten thousand customers can be tracked as having responded to the promotion, the marketer can say with some confidence that the campaign led directly to the responses. By contrast, measurement of other media must often be indirect, since there is no direct response from a consumer. Measurement of results, a fundamental element in successful direct marketing, is explored in greater detail elsewhere in this article.

While many marketers like this form of marketing, some direct marketing efforts using particular media have sometimes been criticized for generating unwanted solicitations. For example, direct mail that is irrelevant to the recipient is considered “junk mail”, and unwanted email messages are considered “spam”.