GMAT stands for Graduate Management Admission Test. Just as the SAT is an admission test for high school students to get admissions into college, the GMAT is an admission test for after-college students to enter into business world by taking admission into a business school.
The vast majority of MBA programs require GMAT score as an essential part of the admission process. Different schools use and judge GMAT scores in different ways. As a general rule, a good score on the GMAT can give you a strong competitive edge in applying to the best business schools.