Main lines refer to the primary routes or pathways used in various contexts, such as transportation, communication, or even in literature. In rail transport, for example, main lines are the major tracks that connect significant cities and regions, facilitating the movement of passengers and goods. In telecommunications, main lines can denote the primary connections for telephone or internet services, ensuring reliable communication. In literature, main lines might refer to the central themes or narratives that drive a story forward, providing structure and coherence to the plot.