If you have a sink in your home, you also have a p-trap. In fact, if you have anything that is draining water, whether a toilet, a shower, or a dishwasher, there needs to be a p-trap. So what is a p-trap? It is the thing that protects your home from sewer gasses that are generated from all the sewage in the pipes. These gasses smell terrible, and being exposed to them can cause a wide range of health issues, not to mention that they will scare away anyone that comes to visit you.
Under your sink, you can easily see the p-trap. It is a sharp bend in your pipe that always is full of water. This water functions as a seal, allowing water and debris to pass through while holding off the gasses that your pipes contain.
As mentioned, even appliances like a dishwasher and an ice-maker would need to have a p-trap between them and the sewer, but they might not always be easily identified.