A general state of well-being and good health in which performance is optimal, i.e. effectively and efficiently
In general, fitness pertains to the state or quality of being fit, e.g. physically or mentally. Physical fitness is a state of health and well-being of an organism, often as a result of good nutrition and exercise. Thus, when an individual is described as physically fit, that means he or she would be capable of performing physical activities, such as sports, chores, and occupational tasks, effectively and efficiently.
Physical fitness from the fitness' biological context is different though. Biological fitness pertains to Darwinian fitness, which is more associated with the reproductive success of an organism. Darwinian fitness measures how successful an organism has been at passing on its genes and its genetic contribution to the gene pool. It is more about the organism's or the population's capacity to survive under prevailing conditions. Thus, the popular phrase "survival of the fitness" coined by Herbert Spencer connotes the capability of an organism or a population to propagate the genes to the succeeding generation. That is, the more likely that an individual is able to survive and live longer to reproduce, the higher is the fitness of that individual.