GMAT uses two ways to present your performance on the test: scores and percentile rank. Together, the two methods are generally refered to as "GMAT score".
Scores The verbal, quantatative sectiosn of the test, and the AWA (essays) are scored separately. These scores are then used to calculate the overall test score. Both section and overrall scores are reported.
Percentile rank Each score is accompanied by a percentile rank which is an indicator of your test performance compared to other test takers. In other words, the higher your percentile rank is the fewer test-takers did better than you. If you have a percentile rank of 71, it means that you did better than 71% of the test takers.
The GMAT is a computer adaptive test which means your score and percentile rank depend not only on the number of correct answers but also on the difficulty of each question.
GMAT scores are valid for 5 years.
What is a good GMAT score?
On average, 500 is considered a passing score to a medium-ranked business program. More reputed programs may ask for 650 and higher. Recently, business programs have been increasing GMAT admission requirements.