Acclimation (also referred to as acclimatisation or acclimatation) is the physical adjustments that an organism makes when it needs to live in a different environment. This is what happens when a person moves to a location with a different altitude, temperature, or humidity level than they are accustomed to.
These adjustments may take some time but eventually they become more comfortable in their new environment. For example, when traveling to a higher altitude a person may experience altitude sickness which occurs as a reaction to lower air pressure and lower oxygen levels in the air. They must take time to acclimate to the environment which usually takes a day or two but sometimes longer.