I loosely define gamification as taking inspiration from game design and behavioral science to influence voluntary user behavior. Game designers and behavioral scientists are asking many of the same questions, it's just that the game designers may not use the same vocabulary or methods for validating ideas. As such, I look to game design as an alternate set of lenses for studying and drawing inspiration for Behavioral Product Strategy.
Other definitions focus too much on mechanics or elements, which ends up leading to the fact that Most gamification sucks and, from my perspective, misses the point. Most people think about gamification as points, badges, and leaderboards. I say that Gamification is not one monolithic thing. In fact, it is a whole domain of study and practice. There could be many genres of gamification beyond the "Foursquare genre."