What is the primary purpose of a trap in plumbing?

The primary purpose of a trap in plumbing is to eliminate odors. Traps are designed to hold a small amount of water, creating a seal that prevents sewer gases and unpleasant odors from entering living spaces. This is crucial for maintaining indoor air quality and ensures that harmful gases do not escape into the home. By retaining water, traps form a barrier that effectively blocks these odors while still allowing wastewater to flow through the drainage system.

Other options might suggest functions related to drainage or pressure, but those do not capture the essential purpose of traps. For instance, while it is true that traps hold water, their primary function extends beyond just holding water for drainage; it specifically addresses the need to keep foul odors at bay.