What is the purpose of a pee trap drain in a plumbing system and how does it prevent foul odors from entering a building?

The purpose of a pee trap drain in a Plumbing system is to prevent foul odors from entering a building. It does this by trapping a small amount of water in the bend of the pipe, creating a barrier that blocks sewer gases and odors from coming back up through the drain and into the building.