The GMAT score is used mainly by business schools to assess a candidate's eligibility for the MBA program.
The GRE score is used mainly by colleges and Universities to assess a candidate's eligibility for a Graduate program in a particular subject.
The GRE is designed and conducted by ETS ( Educational Testing Service), a non-profit institution whereas the GMAT is designed and prepared by GMAC (Graduate Management Admission Council).
The common thing in GRE and GMAT is that they both has analytical writing, quantitative and verbal sections. Moreover, the scores of both are valid till 5 years. Though used in other countries as well, both GRE and GMAT scores are used by institutes, colleges and Universities mostly in the US.
The GRE tests a candidate's proficiency in the following subjects also