What is Pin Up?
1.
An antiquated term for sexually exciting (though often not explicit) material, such as a smiling attractive caucasian women looking back and slightly bent over, or lying back with an arched back.
The acme of the era of pin ups was the American
GI during World War II.
2.
when you get a boner and hide it by pinning it up in your boxers, very useful
I use a pin up whenever I get hard in church.
