The term "SCH 40" is commonly used in the context of pipes, particularly in the construction industry. It refers to a specific type of pipe schedule or thickness that is used in the design and installation of various piping systems.

In simple terms, a pipe schedule is a way of specifying the wall thickness of a pipe based on its nominal size and its intended use. The wall thickness is important because it affects the pipe's strength and durability, as well as its ability to withstand pressure and other environmental factors.

An "SCH 40" pipe schedule indicates that the wall thickness of the pipe is relatively thick, which makes it suitable for a wide range of applications. Specifically, it means that the pipe has a wall thickness of 0.154 inches (3.91 mm) for pipes with a nominal size of 1 inch (25.4 mm) and larger.

Sch 40 pipes are commonly used in a variety of industrial, commercial, and residential applications, including water supply and distribution, heating and cooling systems, gas pipelines, and more. They are also used in the construction of buildings and infrastructure, including bridges, tunnels, and highways.

Sch 40 pipes are preferred over thinner-walled pipes in certain applications because they offer greater strength and durability, which is important when dealing with high pressures or harsh environmental conditions. However, they can also be more expensive and harder to work with, particularly when it comes to cutting, bending, or joining them.