Masterbatch is a solid additive for plastic used for filling the production to lower the cost, coloring or imparting other properties to plastics.
The alternatives to using masterbatches are buying a fully compounded material (which may be more expensive and less open to e.g. color variability of the product), or compounding from raw materials on site.
The use of masterbatches allows the factory to keep stock of fewer grades of the polymer, and to buy cheaper natural polymer in bulk.
Filler materials are particles added to resin or binders (plastics, composites, concrete) that can improve specific properties, make the product cheaper or a mixture of both.