The word used to describe penis, balls, vagina, anus and boobs in a useless and misunderstood way (especialy using the word to "teach" children) and usually what parents tell their children not to let strangers touch
child: momy what are these?
mother: oh sweetums those are your private parts!
child: well... what are private parts?
mother: private parts are the parts of our body that we kept private sweety.
child: why do we have them?
mother: hmmm, well we use them to...
father: to stick my fat cock in your mothers tight pussy son.