To grade means to transfer between one size line to another (or multiple) within the same garment.
Patterns are designed as an excellent starting point for a garment. Everyone’s body is different so it is very possible you should make adjustments to the pattern to make it perfect for your size and shape.
One change you might encounter, is if you fall within multiple sizes of a pattern. Your high bust (includes neck and shoulders) might be a few sizes different to your hip size.
It’s super easy to do, in short…
You’re just going to draw a smooth line from one size line to another.