A percolator is an additional piece for a water pipe that provides a greater measure of filtration within the smoke and the water. The outcome of this is much better inhalation and the cannabis user will have a much smoother experience with less coughing.
Percolators come in a variety of different shapes and sizes and will have many different designs depending on what type of bong is being used. If the user is finding a certain strain of cannabis hard to hit or if their bong is making it not as enjoyable, then a percolator is a good and convenient investment to resolve that issue.
In most cases, percolators are dome-shaped and it can be thought of as basically another water chamber for a bong. The chamber will have water inside of it and it is a secondary filtering system for the smoke. Once you pull the smoke from the bong, it will interact with the water in the bowl, and then once it gets up the tube a little more, it will reach the percolator and go through that process another time.
This gives the smoke two chances to connect through water, and this is what cools it down which results in a more soothing effect for the user. It breaks down the bubbles into sizes that are much smaller because of the pressure inflicted by the percolator. Many people will get the idea that having a percolator on their bong might increase their high. This myth might be misconstrued by the user having a more enjoyable and smooth experience, but a percolator does not increase THC absorption into the body any more than a bong without a percolator does.
Use of Term
My bong has a percolator and it makes the rips I take so much more smooth and enjoyable.