What does the term "pipe fitting" refer to?

The term "pipe fitting" specifically refers to components that are used to connect, redirect, or alter the flow of piping systems. These fittings can include a variety of shapes and types, such as elbows, couplings, tees, reducers, and flanges, which are essential for joining pipes together as well as changing their direction or size within a plumbing or piping system. They play a crucial role in ensuring that pipelines function properly and efficiently transport fluids or gases.

The other options do not accurately define pipe fitting. Decorating materials would not be part of the operational role that fittings play in the piping system. Tools for repairing pipes are distinct from fittings; while they may assist in maintaining or replacing sections of piping, they do not join or modify the pipes directly. Similarly, devices that measure pipe flow pertain to measuring equipment rather than to the physical connections or alterations made within the piping system. Thus, the definition provided in the correct choice captures the essential function and purpose of pipe fittings in various applications.