One who chooses to add to the breadth of their education by embarking upon a program that may award him/her a master's degree, a Ph.D, or no degree at all. While this decision may, under very particular circumstances, lead to a position as a tenured professor in a university, it will most likely lead to a decade or more of delaying the individual's entry to what most people would call the "real" world. Becoming a graduate student allows one to enter the self-perpetuating institution of academia.
Typical sign in a physical sciences laboratory: "Do not feed graduate students and other lab animals."
Grad student: "I'm writing a thesis on the remnants of Victorian culture in modern stereotypes of Transylvania."
Friend: "What are you going to use that for?"
Grad student: "I hope to become an English professor because if I'm lucky, I may one day out-earn high school teachers."