According to Dictionary.com, the term "fitness" means a state of good health and physical ability. It can also be used to refer to the suitability of a concept or object for its intended use.
The word fitness was formed by the combination of the adjective fit and the suffix "ness," which denotes the entire word as meaning "the state of" the word being modified. According to the Oxford Dictionary, it originally appeared in the English language in the 16th century. In biology, fitness can also be referred to as Darwinian fitness, and means the ability of an organism to live and reproduce in an environment, ensuring the continuation of its species.