Grading is the process of creating patterns of different sizes for a garment.
You start from the base size garment.
When you are satisfied with the base garment, you grade the pattern for whatever range of sizes you need.
For example, you might decide that your base size is medium, and you want small and extra small sizes (smaller than the base size), and you also want large and extra large (bigger than the base size).
In VStitcher, you can grade visually or manually, using grade points.