The Reynolds number is a dimensionless quantity used in fluid mechanics to predict flow patterns in different fluid flow situations. It is calculated by dividing inertial forces by viscous forces, helping to determine whether the flow is laminar (smooth) or turbulent (chaotic). A low Reynolds number indicates laminar flow, while a high number suggests turbulent flow. This concept is essential in various applications, including engineering, aerodynamics, and hydraulics. Understanding the Reynolds number helps engineers design efficient systems, such as aircraft and pipelines, by predicting how fluids will behave under different conditions.