A kid comes home from school and says to his mom:
- Mom, I have got a problem.
She says:
- Tell me.
He tells her that the boys at school are using 2 words he does not understand.
She asks him:
- What are they?
He says:
- Well, pussy and bitch.
She says:
- Oh that is no big deal. Pussy is a cat like our little Mittens, and bitch is a female dog like our Sandy.
He thanks her and goes to visit dad in the workshop in the basement. He says to his dad:
- Dad, the boys at school are using words I do not know, and I asked mom and I do not think she told me the exact meaning.
Dad says:
- Son, I told you never to go to mom with these matters. She can not handle them. What are the words?
He tells him:
- Pussy and bitch.
Dad says:
- OK. 
He pulls a Playboy down from the shelf, takes a marker and circles the pubic area of the centerfold, then says:
- Son, everything inside this circle, is pussy.
- Ok dad, so what is a bitch?
- Son, he says, everything outside that circle...