The term 'staircase shape' can refer to a variety of shapes, but the crossword solution for this term is 'SPIRAL, ' which is a shape that winds around a central point in a continuous loop. A SPIRAL staircase is a common example of this shape, as it winds around a central pole and ascends or descends in a circular motion. Spirals are found in nature, such as in the shape of a nautilus shell, and have been used in art and architecture for centuries.