Say, what is growth hacking?

From Wikipedia, growth hacking is as follow:

Growth hacking is a product-focused marketing technique developed by technology startups which uses creativity, analytical thinking, and social metrics to sell products and gain exposure. It can be seen as part of the online marketing ecosystem, as in many cases growth hackers are using techniques such as search engine optimization, website analytics, content marketing and A/B testing. Growth hackers focus on low-cost and innovative alternatives to traditional marketing, e.g. utilizing social media and viral marketing instead of buying advertising through more traditional media such as radio, newspaper, and television.Growth hacking is particularly important for startups, as it allows for a “lean” launch that focuses on “growth first, budgets second.“Facebook, Twitter, LinkedIn, Airbnb and Dropbox are all companies that use growth hacking techniques.