When you're shopping for paints, you'll notice that there are different types of paint with different prices. One thing that affects the price is the "series" of the paint. The higher the series number, the more expensive the paint usually is.
Think of a series as a level or grade of paint. A paint series is determined by the quality and rarity of the pigments used in the paint. Some pigments are more expensive to produce than others, so paints made with these pigments are more expensive too.
For example, a paint with a low series number might only use common pigments like red, blue, and yellow. But a paint with a high series number might use rare and expensive pigments like gold, silver, or a special shade of blue that's hard to find. The paint with the rare pigments will be more expensive because it costs more to make.
So when you're buying paint, you can choose a series based on your budget and how important the quality of the pigment is to you. A higher series of paint may give you richer colors, but it will cost more.