In order to be admitted to postgraduate programs in the United States, applicants must pass the Graduate Record Examination, or GRE. The Educational Testing Service (ETS) is responsible for administering the GRE. The GRE assesses long-term, general-purpose Verbal Reasoning, Quantitative Reasoning, and Analytical Writing abilities that are unrelated to any particular field of study. .
In the US, applicants must take the GRE in order to be admitted to graduate programs. Taking the GRE is probably required if you're applying to graduate school