A cylindrical shell is a three-dimensional geometric shape that resembles a hollow cylinder. It is defined by two concentric circular bases and a curved surface that connects them. The shell has a specific thickness, which distinguishes it from a solid cylinder. This shape is commonly used in engineering and architecture for structures like pipes and tanks. In mathematics, the cylindrical shell method is a technique for finding the volume of a solid of revolution. By integrating the surface area of cylindrical shells, one can calculate the volume of complex shapes formed by rotating a function around an axis, making it a valuable tool in calculus and geometry.