look up any word, like dirty sanchez:
 
1.
What has been seen cannot be unseen.
"Rule 34 on that"

'Just remember Rule 30. You may not like what I have.'
by Mikums July 20, 2008
 
2.
The rule stating that there are no girls on the internet.
*Girl posts picture.*
Not real! Rule 30!
by awesome9 November 03, 2011
 
3.
Rule 30 : TITS or GTFO - the choice is yours.

Usually used on board websites, when a girl posts a picture of herself she has to options they are post a picture of her tits with a time stamp or gtfo.
Simple
How rule 30 works:
*girl post picture of herself*
Anon: Tits or GTFO
by Bossac1234 December 01, 2010