Which term best describes a fitting that tends to adjust the direction of flow within a pipe?

The term that best describes a fitting that adjusts the direction of flow within a pipe is "elbow." An elbow fitting is specifically designed to change the direction of the pipe, typically at angles of 90 or 45 degrees. This allows for efficient redirection of the flow within the plumbing system, making it ideal for navigating around obstacles or achieving a specific layout in pipes.

In contrast, a coupling is primarily used to connect two straight lengths of pipe, allowing for a continuous run of piping without changing direction. A connector serves a similar purpose as a coupling, connecting two pieces of pipe, but may not be as specific in function. A reducer, on the other hand, is designed to connect pipes of different diameters and does not adjust the direction of flow but rather transitions between sizes.

Thus, the elbow is distinct in its primary function of altering the path of fluid movement within a plumbing system.