Form and shape can be described in two or three dimensions. Two-dimensional forms have width and height, while three-dimensional shapes also have depth. Forms can also be categorized as organic or geometric. Organic forms are irregular and asymmetrical, often occurring naturally, while geometric forms correspond to regular shapes like squares and circles. Two-dimensional forms use techniques like line, value, hue, texture, and negative space to create the illusion of three-dimensional shapes and spaces.