To me health is adaptability.
If I am healthy then I am adaptable.
From a cellular viewpoint, this would mean that if resources of biological energy are sufficient, then I will be able to meet or adapt to any number of life's arising demands.
If these resources are replete, then I will enjoy life with flexibility and optimism. I will be able to withstand any number of ordinary "stressors" with spunk. I will, for the most part, be able to look at whatever I do, as play.
So healthy means being able to have a shit-ton of fun, in a variety of contexts.