Certainly a book for prospective scientists ought to explain what science is. Still, despite numerous books that treat the philosophy, character, and practice of science, there is no agreed-upon nor clear-cut and unambiguous definition of science. This holds not only for the many fields of study that have adopted methods patterned on those of the natural science, e.g., social science, psychology, economics, managerial science, and military science, but also for the natural sciences themselves. In a broad sense one might define science as the activities aimed at understanding the world around us, but it could be well argued that the arts, humanities, and many other endeavors in modern society likewise aim at understanding of the world, albeit understanding of a different sort than that sought in the natural sciences. So let's focus on the practice of natural science, which might be defined as the activities aimed at understanding of the natural world.