It often amazes me that FITNESS is a multi-billion dollar industry... Yet a good, concise and universal definition of fitness is difficult to nail down.
Just ask an individual participating in a physical fitness plan, as well as someone in the health sector for that matter, to provide you with an obvious meaning of health.
You'll more than likely be met with the "deer caught in the headlights" gaze accompanied by absurd stammering.
Should you get an answer, it will most probably be slanted toward the particular proficiency of the person asked.
For example...

A marathon runner will define fitness in terms of cardiorespiratory and muscular endurance... A power-lifter is going to define fitness in conditions of absolute strength... A bodybuilder will define fitness in terms of muscle size and colon broom instructions (how you can help) definition... etc.
But the overwhelming majority of people taking part in a physical fitness program are not professional athletes concerned with the improvement of just one physical ability.
Thus, basing your definition of fitness in one specific physical ability does not result in a universal definition of health and fitness.