According to Oxford dictionary:

con·tent mar·ket·ing

noun

A type of marketing that involves the creation and sharing of online material (such as videos, blogs, and social media posts) that does not explicitly promote a brand but is intended to stimulate interest in its products or services. Social media is an integral part of content marketing"

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We like dictionary.com's version better:

noun

Marketing that tries to attract customers by distributing informational content potentially useful to the target audience, rather than by advertising products and services in the traditional way: content marketing through blogs and email newsletters.