Which shape is defined as having a circular base and top connected by walls?

The shape that is defined as having a circular base and top connected by walls is indeed cylindrical. A cylinder features two parallel circular surfaces (the top and bottom) that are aligned and connected by a curved surface wrapping around the sides. This definition emphasizes the circular nature of the bases and the straight, vertical walls that connect them.

In contrast, the other options describe different shapes. A rectangular shape would involve four straight edges and right angles, distinctly lacking the circular elements associated with a cylinder. A conical shape tapers from a circular base to a single point at the top, thus having a different geometric structure compared to the consistent diameter of a cylinder. Lastly, an elliptical shape is defined by an elongated circular contour and does not conform to the structure involving parallel bases like a cylinder does. This understanding solidifies the reason why the cylindrical shape is the correct answer in this context.