I have been involved in business-to-business media for many years and in, in the beginning, we mostly only had print publications to reach targeted audiences. It worked very effectively and it still does. Then, about in the 1990's digital media became an important part of the b-to-b marketing plans of many advertisers.
That portion of the business, digital media, continues to evolve. There are now many ways to reach your target audience including print publications, e-newsletters, website ads, webinars, and more. Add to that mix content marketing.
I am in the process of reading a book by author, Joe Pulizzi of the Content Marketing Institute titled Epic Content Marketing, here is a link. In the book, Joe gives this formal definition "Content marketing is the marketing and business process for creating and distributing valuable and compelling content to attract, acquire, and engage a clearly defined and understood target audience with the objective of driving profitable customer action."
The way that I understand content marketing is that it involves a company using specific content or information about products or services to describe how the company can work with the reader/prospective customer to add value to their products, machinery, enterprise, process, or business in general. In other words, it offers solutions, solves problems, of gives customers a source to partner with and tells them how and why.
I hope that I described this correctly; it is a work in progress. Please contact me for more information.