From Pipes, Artisans and Trademarks, by José Manuel Lopes
Terminus is a brand by EWA, called the "terminus system", to cool the smoke as it passes down the shank. Many of the brand's stems are in horn. The same brand name was produced by the Gradclémetn-Gauteron factory.
Here’s how it works: The shank is drilled wide and has an inner tube in the center of this chamber. On both sides of the inner tube are two draw holes into the bowl. The stem has a thinner inner tube that fits inside the larger tube that's in the shank. The smoke first goes through the two draw holes and into the chamber where the tar and impurities remain. Then the smoke it sucked through the thicker shank tube and up the stem's inner tube to end in the smoker's mouth.