The definition of Growth hacking on Wikipedia is the original and best in this case I think, let me know if you know the original source 🙂 It shows how it combines marketing and sales, but doesn’t emphasise new product development and value proposition testing.
Growth hacking is a process of rapid experimentation across marketing funnel, product development, sales segments, and other areas of the business to identify the most efficient ways to grow a business.
Sean Ellis, is arguably the leading authority on Growth Hacking since he led the exponential growth at Dropbox, LogMeIn, Lookout, and Eventbrite and posted one of the first articles on the topic in 2010, Find a Growth Hacker for your startup.
He founded GrowthHackers.com, a community sharing examples of growth hacking techniques, published the book Hacking Growth and runs the Breakout Growth podcast.