What does eating clean mean?

Eating healthy is a concept that seems to have been adopted widely by society at large in the last couple of years. For some reason, however, its definition is very blurry and unclear to the wide majority of people who think that eating healthy is the correct way to live life.

And, if you are anything like me, you are part of those confused people, but want to dig deeper into the fundamental concepts of nutrition (the 20% representing 80% of the fundamental knowledge in the field), in order to understand what eating clean may mean, and whether it is the appropriate long term strategy to nutrition when it comes to living a healthy, balanced existence, while training like an athlete.