noun

• (uncountable) The process of adapting something or becoming adapted to a situation; adjustment, modification.
  "To sum up, the Furka-Oberalp Railway is a good example of the adaptation of the rack-and-pinion system to a main line over mountainous terrain."
• (countable) A change that is made or undergone to suit a condition or environment.
  "It's staggering because these adaptations to your schedule can dramatically change your life forever."
• (uncountable, evolutionary theory) The process of change that an organism undergoes to be better suited to its environment.
  "ACCLIMATIZATION, the process of adaptation by which animals and plants are gradually rendered capable of surviving and flourishing in countries remote from their original habitats, or under meteorological conditions different from those which they have usually to endure, and at first injurious to them."
• (countable, evolutionary theory) An instance of an organism undergoing change, or the structure or behavior that is changed.
  "This is the very method adopted, in the structure of the eye, to produce a perfect picture on the retina; it is an adaptation to the laws of light, and the property of color, in natural objects."