An ___ is a ___ that makes a living thing better able to___
_in its surroundings.

An adaptation is a trait that makes a living thing better able to survive in its surroundings.

Explanation:

The unique characteristic or trait which an organism develops in order to adapt to its ecological surrounding or habitat is called as adaptation.  

Adaptation is a result of evolutionary processes which arises as a need for survival and makes it environmentally fit.

Adaptive traits are mutations or changes happening in the inherited traits acquired over generation after generation through natural selection. When these changes are acquired by almost the entire population of a species, these traits become the unique adaptation traits of that particular species.

Adaptations can take place through physiological, behavioral, or structural changes.

Plants adapting to desert conditions by undergoing structural changes is structural adaptation .

Birds migrating to long distances to avoid extremely cold or other unfavorable weather conditions exhibits behavioral adaptation.

The ability of polar bears to hibernate during cold winter periods is both a physiological and a behavioral adaptation