Exology or xenology is a term which refers to the scientific study of any type of subject matter or phenomena that is alien to an observer's homeworld or frame of reference. A scientist of this field is an exologist or xenologist.
Notable subsets of this field are exobiology, astrobiology or xenobiology (the study of alien biology), exozoology or xenozoology (the study of alien animals) and exogeology or xenogeology (the study of alien geology).
In the 24th century, Eric Baldwin was one of the Federation's most important exologists. (TNG novel: Boogeymen)
Doctor Kila Marr was a xenologist, and the foremost expert in the Crystalline Entity. (TNG episode: "Silicon Avatar")