The equation A1V1 = A2V2 represents the principle of conservation of mass in fluid dynamics. Here, A1 and A2 are the cross-sectional areas of a pipe at two different points, while V1 and V2 are the fluid velocities at those points. This relationship shows that if a fluid flows through a pipe that narrows or widens, the product of the area and velocity remains constant. This principle is crucial in understanding how fluids behave in various systems, such as water pipes or airflow in ducts. It helps engineers design efficient systems by predicting how changes in area affect fluid speed, ensuring optimal performance.