It’s an adjective; it means able to adjust to new conditions or capable of being modified for a new purpose. It can be applied to both people and objects and some authorities say that being adaptable, able to cope with changing conditions, is why humans are the dominant life form on earth.
It is frequently used in the workplace to describe someone who can handle anything and is capable of taking on the jobs that would have others scratching their heads until they got splinters under their fingers. It is also used to describe members of the British armed forces, one reason, perhaps, why they are the best in the world.
A large life change that happens as the result of a social falling out. It usually happens during adolescence, where a person may need to think about the person there are in an effort to make themselves more socially adaptable. They may be extremely quiet or socially awkward while they are still learning, as they may need to relearn large amounts of social skills, as well as may be deeply engrossed in thought and not focused on the world around them. Many people that experience this phase believe that they are the only person on Earth that have experienced it, although, in reality, a lot of people will experience it.
Guy 1: What is Willie doing over there by himself? Didn’t he have a lot of friends last year?
Guy 2: He did, but he fell out with them and is out of friends right now. I’m sure he’s just going through an adaptability phase. He’ll have more friends soon.