I think being healthy is living a normal life with as few self destructive behaviors as possible. We are all healthy to some degree, and we all have different body types and physiques. When I say self destructive behaviors, I'm not just referring to depressed people on suicide watch. Habits like smoking, drinking, doing drugs, overeating are all pretty unhealthy because they change they way the body is intended to function.
Don't get me wrong, I have nothing against people who do these things, and I've been known to have a drink here and there as well. In terms of health though these habits hurt the body more than help.
Smoking for instance pollutes the lungs forcing them to work harder to intake the same amount of air. Granted I know it's a slow process, but it still happens.
Alcohol is unhealthy not only because it impairs our decision making abilities, but when taken in excess, it can cause damage to our organs.
Drugs are unhealthy because some of them can addictive by changing your body's chemistry so it can't function without the drug. Drugs are also unhealthy because they can mess with the mind which can result in dangerous behavior.
Overeating is unhealthy because normally a body eats to attain energy which we usually burn off whether at work or play. When we overeat, rather than burning off the energy, our bodies store it as fat. The more of it that is stored, the harder it becomes to be mobile. It also becomes even harder to burn off the stored fat.
I'm sure there are plenty of unhealthy behaviors people engage in, but these were the ones on the top of my head. As I said, I believe we are all healthy to a degree, but when we engage in unhealthy behaviors, we are decreasing our health.