Understanding Allochthonous vs Autochthonous: A Guide to the Differences and Applications

Allochthonous (Greek: allos, "other" and chthonic, "earthy") refers to something that is derived from outside of a particular region or system, as opposed to autochthonous (Greek: auto, "self" and chthonic) which refers to something that is derived from within.
In geology, allochthonous refers to rocks or sediments that have been transported and deposited in a new location, often by tectonic forces such as plate movement or faulting. In contrast, autochthonous rocks are those that have formed in place, without being transported.
In biology, the term allochthonous is sometimes used to describe organisms that have been introduced to a new environment, either intentionally or unintentionally, and are living outside of their native range. For example, the term might be used to describe non-native species that have been introduced to a new ecosystem through human activity, such as the introduction of non-native fish to a lake or the release of non-native animals into the wild.
In general, the terms allochthonous and autochthonous can be used to describe any system where there is a distinction between materials or organisms that are derived from within a particular region or system, versus those that are derived from outside of it.