The horizontal distance from the crown weir of a trap to its vent is known as the __________.

The term describing the horizontal distance from the crown weir of a trap to its vent is known as the "trap arm." The trap arm is a critical component in plumbing systems as it connects the trap to the vent stack, ensuring proper venting and preventing the siphoning of water from the trap.

The trap arm allows air to flow into the plumbing system, which helps maintain the water seal in the trap and prevents sewer gases from entering the living space. The correct distance and orientation of the trap arm are essential for efficient drainage and ventilation, as it must adhere to specific plumbing codes to function properly.

In contrast, concepts like a trap baffle refer to elements that may provide separation of water flow in certain traps, while a vent pipe is a part of the system that allows for air circulation but does not define the distance from the weir to the vent. Similarly, the siphon arm pertains to the dynamics of fluid movement in siphoning actions rather than establishing measurements related to trap installations. Thus, the term "trap arm" accurately identifies the defined horizontal distance relevant to plumbing practice.