Definition From Google:
a change or the process of change by which an organism or species becomes better suited to its environment.
What I think:
I think that adaptation a species that has changed the way the live in their environment. They have to be living there, or have been living how they live for hundreds or millions of years, the species can not just change the way they live and move on.
One animal who I think adapts well is the Diving Bell Spider. They live their entire life under water in a air bubble. They only have to come up to the surface once a day to fill their air bubble. Except for that they live under water. The air bubble is made of web that they make to make webs.