Content marketing is the publication of material designed to promote a brand, usually through a more oblique and subtle approach than that of traditional push advertising. The essence of good content marketing is that it offers something the viewer wants, such as information or entertainment.
Content marketing can take a lot of different forms, including YouTube videos, blog posts and articles. It shouldn't really seem like marketing -- in some cases, in fact, it should only be identifiable as marketing because the advertiser is identified as the content provider. Native advertising, for example, is content integrated with a website or service in such a way that it doesn't stand out from other material presented there in terms of content, format, style or placement. Ideally, content marketing provides the consumer with valuable information, the publisher with content and the advertiser with a larger audience and a stronger brand.
The Federal Trade Commission (FTC) recently updated its guidelines for advertising online, known as the dot com disclosures. FTC guidelines applicable to content marketing include stipulations that advertising claims must be truthful and supported by evidence, and testimonials and endorsements must be honest opinions of actual customers. In the event that further information is required to ensure that a claim is not misleading, that information must be clearly and conspicuously disclosed, ideally along with the claim rather than separately. All content provided must be accurate and unbiased and should explicitly state that it was provided by the advertiser.
See a video about the history of content marketing: