In plumbing system, a trap is located below plumbing fixtures to prevent sewer gasses from entering the building. You will see in the attached video from a recent home inspection that there is what is referred to as an "S" Trap. In many locations, plumbing codes do not allow "S" Traps as they are prone to siphon out the water seal even if properly vented, thus allowing sewer gassed to escape into the building. The accepted type of trap is called a "P" Trap. Your home inspectors report should document where "S" traps are in use.