Pin-up girls are like pictures of ladies that you might see in your grandpa's garage or in a tattoo shop. They were really popular in the olden days and they're usually drawn or painted to be really pretty and kinda sexy.
Pin-up girls usually wear cute outfits like polka dot dresses or sailor outfits, but sometimes they don't wear very much clothing at all. They might be flexing their muscles or sitting on a bomb or something, which might seem a little silly.
Some people collect pin-up girl art or use it to decorate their homes. But it's also important to remember that not everyone thinks pin-up art is appropriate. Some folks think it's disrespectful to women or promotes unrealistic expectations for how women should look or act.