Form is one of the basic building blocks of art and refers to a three-dimensional shape that takes up space. There are two categories of forms: geometric forms like spheres, cubes, and cylinders that are precise mathematical shapes, and organic forms that are free-flowing and irregular like leaves or clouds found in nature. In art, forms can be depicted in two ways - as real, sculptural forms or as implied forms using techniques like shading to create the illusion of depth and volume on a two-dimensional surface. Examples of different types of three-dimensional forms include sculptures, ceramics, architectural structures, and earthworks.