A P-trap is a plumbing fixture commonly installed with kitchen and bathroom sinks that prevents clogs. It can be constructed of either metal or PVC.
A P-trap resembles the letter "P" if it were rotated 90 degrees. If debris flows down the drain and into the pipe system, the P-trap collects the debris to prevent it from coursing through the rest of the plumbing. It is also used to keep sewer gases from flowing backward into the home. Sewer gases can cause offensive odors, explosions and other issues.
Up to three sinks can be connected to the same P-trap. The best applications for P-traps are sinks or other utilities that are used on a regular basis.