What shape is created by four straight lines joined end-to-end?

When four straight lines are joined end-to-end, they form a closed figure with four sides. This specific type of shape is known as a quadrilateral. A quadrilateral can take various forms, including squares, rectangles, trapezoids, and other types, as long as it consists of four vertices and four edges.

In contrast, a circle is defined as a continuous curve with all points equidistant from a central point, which cannot be formed by straight lines. A triangle, having only three sides, cannot arise from four lines. Similarly, while squares and rectangles are specific instances of quadrilaterals (involving right angles and equal sides, respectively), they do not encompass the broader category of all four-sided shapes. Thus, the most accurate and comprehensive term for a shape with four straight sides is indeed a quadrilateral.