Any bizarre, outlandish fetish. Usually a periox is an act of sodomy such as bestiality.

For instance:
Shemale fetishes
Foot fetishes
Sock fetishes
guy-analing-horse fetishes

are all considered to be perioxes whereas

granny fetishes
black guy & asian girl fetishes

are not perioxes.

The safeguarding of Earth and other worlds from biological cross-contamination (i.e. billionaires with too much time on their hands).

Also known as “planetary protection.” Planetary protection / quarantine “reflects both the unknown nature of the space environment and the desire of the scientific community to preserve the pristine nature of celestial bodies until they can be studied in detail.”

There are two types of interplanetary contamination. Forward contamination is the transfer of viable organisms from Earth to another celestial body. Back contamination is the transfer of extraterrestrial organisms, if such exist, back to the Earth's biosphere.