Fitness is defined as: good physical condition; being in shape or in condition.
A more detailed definition of fitness is: a unit-less measurement of the replication ability of a particular creature in a specified environment. By itself, fitness has little intrinsic meaning, but when compared to that of another creature it gives a ratio of their respective replication rates. Specifically, to calculate fitness, we take a creature’s merit and divide it by its gestation time. (fitness = M/tg). Since merit increases exponentially with the number of tasks acquired, fitness is best described by the log of its actual value (see also Inferiority).
Fitness is really a measure of something you feel, how easily you can run without tiring, skate or jump with ease repeatedly. It relates to your physiological efficiency. Attained fitness grows with training and decays away generally at about 3% per day if you do not maintain a level of training appropriate to the fitness state you presently have.
Fitness can be achieved in a number of ways. It can be attained and maintained by having a healthy diet (e.g. low calories, no fast food), getting plenty of exercise (e.g. pilates, home gym, weight lifting) and having confidence in yourself. Fitness not only helps your overall health, it can help prevent against cancer and can help you look your best.