GRE stands for Graduate Record Examination. It is one of the exams for eligibility to MS Universities in USA and a few other countries it varies from country to country. The exam has a maximum score of 340 with 260 being the lowest. There are 2 sections Quantitave and Verbal of 170 marks each. Everyone is eligible for GRE that is there is no eligibility for the Exam and the score is valid for 5 years.

Dear Ankit,

It is an international test conducted by ETS for admission to graduate courses in USA and some other countries. It's score is used for entry to Masters or PhD courses abroad, specifically in universities in US and Canada

Aspirants interested in pursuing a higher education, especially Master's degree, specialised Master's course, MBA or a PhD degree can appear for the GRE. 

There is no specific eligibility criteria to pursue postgraduate programmes. You have to fulfill the admission criteria for the institutes/ universities you are applying to. 

Make sure you complete your under graduate course. 

To know in detail you can refer below link

https://studyabroad.careers360.com/articles/gre

Good Luck!!