Fitness
Fitness may refer to:

Physical fitness, a state of health and well-being of the body
Fitness culture, a sociocultural phenomenon surrounding exercise and physical fitness
Fitness (biology), an individual's ability to propagate its genes
Fitness (cereal), a brand of breakfast cereals and granola bars
Fitness (magazine), a women's magazine, focusing on health and exercise
Fitness and figure competition, a form of physique training, related to bodybuilding
Fitness approximation, a method of function optimization evolutionary computation or artificial evolution methodologies
Fitness function, a particular type of objective function in mathematics and computer science
"Fitness", a 2018 song by Lizzo

See also
FitNesse, a web server, a wiki, and a software testing tool
Survival of the fittest