1. slang An extremely dirty or untidy room or area. Likened to the literal pens where pigs live, typically covered in mud and filth. If this pigpen isn't cleaned by the time I get home, you'll both be grounded for a week! I left the kids alone while I was gone, and the house was a total pigpen when I came back.

2. slang A police station or headquarters. ("Pig" is a common derogatory slang term for a police officer.) Suddenly, all the cops went back into their cars and sped back to the pigpen. They're keeping the evidence locked up at the pigpen.

3. slang A hash mark (#), known as a "pound sign." Make sure you put a pigpen in front of the number when you enter it into the spreadsheet.