Solid lines are continuous lines that do not have any breaks or gaps. They are commonly used in various contexts, such as in road markings to indicate lanes or boundaries. In mathematics, solid lines can represent functions or relationships on a graph, showing a direct connection between points. In art and design, solid lines can create shapes and define spaces, providing structure to a composition. They are often used in blueprints and technical drawings to represent edges and outlines clearly. Solid lines convey a sense of stability and permanence in visual communication.