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Content Marketing means creating and sharing valuable information to attract and convert prospects into customers, and customers into buyers. The type of content you share should be closely related to what you sell; in other words, you’re educating people so that they know, like, and trust you enough to do business with you. 

Then there's the Wikipedia defintion
Content marketing is an umbrella term encompassing all marketing formats that involve the creation and sharing of content in order to attract, acquire and engage clearly defined and understood current...