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.