An adaptation is a heritable trait that increases an organism's survival and reproduction in its environment. It's important to understand that adaptations are not just any trait, but specifically those that provide a selective advantage in a given environment.

Here's a breakdown:

* Heritable: Adaptations are passed down from parents to offspring through genes.

* Survival and Reproduction: Adaptations help organisms survive to reproduce and pass on those advantageous traits.

* Selective Advantage: Adaptations are advantageous because they increase an organism's chances of surviving and reproducing compared to individuals without the trait.

For example, a giraffe's long neck is an adaptation that helps it reach leaves high in trees, giving it a food source that other animals can't access. This adaptation allows giraffes to survive and reproduce more successfully than giraffes with shorter necks.

Therefore, adaptations are:

* Inheritable: They are passed down genetically.

* Functional: They increase survival and reproduction.

* Selective: They provide an advantage in the environment.