Here are some examples of words with the root "allo-":
* Allotype: A variant form of a protein.
* Allograft: A tissue transplant from one person to another.
* Allometry: The study of how the size and shape of an organism change with growth.
* Allopathy: A system of medical practice that treats disease with drugs that have effects opposite to the symptoms.
Therefore, "allo-" generally indicates something that is different from the norm or something else.