Rule 34 states:

If it exists, there is porn of it.

It was soon followed by Rule 35:

If no such porn exists, it will be made.

Rule 34 is generally said to be spawned from the 4chan online community, (but there are memes/rule-34">other possibilities for the origin of Rule 34) and its somewhat facetious Rules of the Internet. It seems to me likely that the cartoon from Zoom Out Productions embedded to the left, was in fact the original inspiration, and that it was itself turned into a meme and propagated by 4Chan. I note, for those who are blessedly unfamiliar, that 4Chan at its heart an anonymous no-holds-barred image-posting community, responsible for propagating several Internet Memes, not the least of which are LOLCats, and Rule 34.

Rule 34 is typically interpreted in the context of fiction, and media, particularly television shows and films that spawn fan fic, though there are those who think that, well, everything has potential for porn, whether it's in the Sears Roebuck catalog or not. The subtext of Rule 34 and related rules is that ultimately the Internet survives because of niche communities, whether or not said communities actually revolve around porn. I note that niches like dragons having sex with cars (not graphic) exist quite handily, and demonstrably support the basic premise of Rule 34.