To me, bodybuilding is a lifestyle that allows you to achieve top fitness, lose weight, and get into any sort of shape that you want to. Regardless of what your fitness goal is, you can achieve it using bodybuilding. You can use bodybuilding to simply be nicely toned and defined, or use it to gain enough size to actually compete in a bodybuilding show.
So in my opinion, anyone that lifts weights, performs cardiovascular exercise, and follows a proper bodybuilding diet day in and day out is a bodybuilder because they are using bodybuilding in order to achieve a specific fitness goal. Some of us eventualy decide to step on stage while most people don't; but regardless, anyone who follows the lifestyle is a bodybuilder in my book.
If you are contemplating getting started on a new bodybuilding program but do not know how, please take a look at my article on How to Get Started in Bodybuilding.