The phrase throws most people off. All it means is 'new fangled and innovative ways to convert users to paying customers`. The ultimate goal of a "growth hacker" is to convert users, via some clever way. The obvious techniques like funnels/mailresponders/sharing/retargeting/onboarding do work, but they're not good enough. I know it's cliche - but growth hacking basically means "thinking outside the box" to convert users.
User Personas are the hot new thing now, where startups try to break a userbase into separate 'types' of typical users. E.G; User set A is young, trendy. User set B is hobbyist. User set C is B2B (business to business), etc