The GPA can be used by potential employers or further post-secondary institutions to assess and compare applicants. A Cumulative Grade Point Average is a calculation of the average of all of a student's grades for all semesters and courses completed up to a given academic term, whereas the GPA may only refer to one term.
Keith Hoskin argues that the concept of grading students' work quantitatively was developed by a tutor named William Farish and first implemented by the University of Cambridge in 1792. Hoskin's assertion has been questioned by Christopher Stray, who finds the evidence for Farish as the inventor of the numerical mark to be unpersuasive. Stray's article clarifies the complex relationship between the mode of examination (testing), in this case oral or written, and the varying philosophies of education these modes imply, both to teacher and student. As a technology, grading both shapes and reflects many fundamental areas of educational theory and practice.
It is difficult to convert GPA to letter grade without knowing exactly which countries you are asking about as every country has their own grading system, either using GPA or Letter grades, or for example of the UK a mixture of both as well as other systems, such as the degree grading system. To give an approximated answer to your question, I will use the scenario that you wish to have a United States of America 2.5 GPA converted to that of the United Kingdom Letter system, both at the equivalent level to UK high school exams.
Therefore a US 2.5 GPA is equal to a UK letter grade of between a C+ which is suggest as being the same as 2.3 GPA and a B- which is seen as the equivalent of a 2.7 GPA.