GMAT (Graduate Management Admission Test) is used by MBA and PhD programs in the United States, Canada, Britain, Australia and other countries (including Turkey). Many English Master's (especially MBA) and PhD programs require the test.
More than 7000 graduate programs around the world use GMAT as an acceptance criteria. You can find the list of educational institutions where the exam is accepted at the following link: https://www.mba.com/articles-and-announcements/articles/gmat-exam/gmat-accepting-programs-around-world
The test measures analytical writing, integrated reasoning, quantitative and verbal ability.