The "Red Line" typically refers to a specific route in a public transportation system, such as a subway or metro. For example, in cities like Boston and Los Angeles, the Red Line serves as a major transit line, connecting various neighborhoods and key locations. It is often characterized by its red color on maps and signage, making it easy for riders to identify. In addition to public transit, the term "Red Line" can also refer to a metaphorical boundary or limit in various contexts, such as politics or personal relationships. Crossing this line often signifies a serious consequence or a point of no return, emphasizing the importance of boundaries in different aspects of life.