"Biological experimentation done to improve the qualities or capabilities of living organism especially by individuals and groups working outside a traditional medical or scientific research environment."
Or more simply:
"Such experimentation done on one's own body."
We quite like Dave Asprey's definition of BioHacking which puts it more succinctly:
"To change the environment outside of you and inside of you so you have full control of your biology, to allow you to upgrade your body, mind and life.
In this article, we're going to introduce you to some of the leading BioHackers and individuals who are opening areas of conversation about aging and longevity.