The weight of a grade determines how much that grade affects your overall average. A grade with a higher weight has more influence on the average than a grade with a lower weight.
Weight is a number that indicates the importance of a grade. Commonly used weights are 1, 2, 3, or 0.5. For example, a major test may have a weight of 2 or 3, while a small quiz or oral examination has a weight of 1.
Example: If you have a 3 from a major test (weight 2) and a 1 from a small quiz (weight 1), the 3 from the test affects the average twice as much as the 1 from the quiz.
Thanks to weights, a major test or important exam has more influence on your average than a regular quiz or small test. This is fair because students usually prepare more for major tests and they cover more material.