What does the term "grade" refer to in plumbing?

The term "grade" in plumbing specifically refers to the fall or slope of a line of pipe in relation to a horizontal plane. This concept is crucial for ensuring proper drainage and flow within plumbing systems. When pipes are installed with the appropriate grade, it allows gravity to assist in moving water and waste efficiently through the system, preventing clogs and backups.

Establishing a proper grade is essential for both drain lines and vent lines, as it impacts the effectiveness of wastewater removal and ventilation necessary to maintain the plumbing system's function. The slope must be within certain specifications, depending on the pipe diameter and type to ensure optimal performance and compliance with plumbing codes.

Other choices do not accurately define "grade" in the context of plumbing, making the choice regarding the fall of a pipe the most appropriate.