Graduate students may choose to self-fund their graduate studies. If they are interested in finding financial assistance, there are three sources: (1) Fellowships, (2) Assistantships, and (3) Scholarships.
Fellowships come from a wide variety of areas, and are funded very specifically after an application process. Fellowships typically waive tuition and provide graduate students a stipend. Depending on the fellowship, it may be funded for the entire graduate program, or for a finite period, at which time the student then goes onto an assistantship. Learn about the various fellowships the Purdue offers at: http://www.gradschool.purdue.edu/funding/