In medicine, zoonotic describes a disease that can be spread from animals to humans. If a rabid dog bites a person, the person may become infected with rabies, which is a zoonotic virus.
Zoonotic comes from the noun zoonosis and its Greek roots, zōon, "animal," and nosos, "disease." The majority of diseases that affect humans started out in animal populations, but only the ones that pass directly from animals to people are considered zoonotic. One of the things that illnesses such as the Ebola virus, ringworm, and Lyme disease have in common is that they're all zoonotic.