Fetish involving someone going through a woman's vagina and into the womb, usually coming back out later on. Pretty obviously restricted to cybersex and fantasy art or writing.
Some people on the Internet get turned on by unbirth.
by Carne Largo October 15, 2003
A mysterious new enemy from Kingdom Hearts: Birth by Sleep. All we know is that they move fast, are blue, and have piercing red eyes.
"What are the Unbirth?"
by Grimrock August 03, 2008