About the Tests
Admission to the best MS programs in the US is based on the complete profile of a candidate / prospective student. This profile is a function of numerical and subjective parameters. Numerical parameters include academic grades, GRE score, and number of years of work experience. Subjective parameters are more complex and include academic potential, quality of work experience, unique perspective a candidate may have, cross cultural experience, leadership, team skills, the diversity a candidate may add to his peer-group at the university, etc.
As students applying to MS programs in the US come from diverse countries, backgrounds, academic-subjects and systems of education, so GRE provides a common objective numerical yardstick to compare all candidates.
Top schools receive a huge number of admission applications, so an easy way to weed out/reject a bulk of candidates is to use a minimal score on the GRE as a qualifier. This cut-off value of GRE score is higher for more competitive universities and changes almost every year.