" The term “growth hacker” has many different meanings for different people, but I’ll define it as I have come to understand it: A growth hacker is someone who has thrown out the playbook of traditional marketing and replaced it with only what is testable, trackable, and scalable. Their tools are emails, data targeting, blogs, and platform APIs instead of commercials, publicity, and money. While their marketing brethren chase vague notions like “branding” and “mind share,” growth hackers relentlessly pursue users and growth—and when they do it right, those users become evangelists for products, bringing more users with them. Growth hackers are the inventors, operators, and mechanics of a self-sustaining and self-propagating growth machine that can take a company not just from zero to one, but from one to a hundred or a hundred million. "

― Ryan Holiday , Growth Hacker Marketing: A Primer on the Future of PR, Marketing, and Advertising