A Moody chart is a graphical representation used in fluid mechanics to determine the friction factor for flow in pipes. It helps engineers and designers calculate pressure losses due to friction in various types of flow, including laminar and turbulent flow. The chart is based on the Darcy-Weisbach equation and incorporates factors like pipe roughness and flow velocity. The Moody chart plots the Reynolds number against the friction factor, allowing users to find the appropriate values for different flow conditions. It is a valuable tool in hydraulic engineering, aiding in the design of piping systems for water, oil, and gas transport.