Its actually pr0n, and its spelled this way so that it doesn't show up when someone searches the word "porn".

It was introduced as a masking tool to prevent people from logging your involvement in less than reputable activities. Much like the original intent behind 1337 speak itself.

Similar words for divisions of pr0n that are still in use include:
R@ygold - (pedophylia)
qwerty - (bestiality)
showme - (voyuer)
rorikon/lolikon - (anime child)
momashi - (incest)
BBW - (Big Breasted Women)
etc...

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.

1337 (leet) for pornography. usually the o is replaced by the digit 0, ie: pr0n.

The second most searched for word on the internet

What you type in instead of porn as an excuse when your on the internet and you wanna see tits but dont wanna get in trouble

You know when you want to masturbate when you look up porn, you type it in fast and you misspell porn, insted getting pron.

l337 for porn.