Final answer:
The term for an abstract form, such as a railroad turnbridge, is Abstraction. This art style uses shapes, colors, forms, and textures to create an effect rather than to represent reality accurately.
Step-by-step explanation:
The term that describes an abstract form, such as a railroad turnbridge, is Abstraction. Abstraction in art refers to the concept where the artwork does not attempt to represent external reality accurately but seeks to achieve its effect using shapes, colors, forms, and textures. A good example to understand abstraction is by contrasting it with its opposite, Representation, which strives to depict figures and subjects in a realistic manner, resembling their appearance in real life. When you look at a more abstract piece, details are omitted, and the subject is often simplified or rearranged without regard to how realistically it conveys the actual image.