| Possessing all three spatial dimensions: height, width, and depth. A sphere, a cube, and a pyramid are all simple geometric three-dimensional figures. When contrasted with a four-dimensional object, a three-dimensional object does not change with time.
In a literary context, a three-dimensional character is one possessing ambitions, motives for those ambitions, and a clear history to explain those motives. Three-dimensional are the most believeable kind and take the most time to write, which is why your average writer will settle for the two-dimensional sort. | 
