Red Line

The Red Line typically refers to a major transportation route or line that is often a key transit corridor in a city. For example, in Washington, D.C., the Red Line is a primary subway line running through the city and surrounding suburbs, connecting many important neighborhoods and destinations. In financial contexts, "red line" can also mean a limit or boundary that should not be crossed. Overall, the term generally denotes a significant, well-defined pathway or boundary within a particular system or context.