The term that best describes a specially developed characteristic that enables an organism to live in a specific environment is adaptation.

Here's why:

* Adaptation refers to a trait that has evolved over time to help an organism survive and reproduce in its particular environment. These traits can be physical (like a thick fur coat for animals in cold climates) or behavioral (like migration patterns for birds).

Other terms that are related but not as specific include:

* Evolutionary trait: This refers to any characteristic that has evolved over time, but it doesn't necessarily imply a specific benefit for a particular environment.

* Phenotype: This is the observable characteristics of an organism, including both physical and behavioral traits. However, not all phenotypes are adaptations.

* Trait: This is a general term for any characteristic of an organism, but it doesn't specify whether it has evolved specifically for a particular environment.