A 16-piece hole saw set is a kit designed to drill large-diameter, clean holes in various materials. The "16 pieces" typically refers to a combination of hole saw cutters, the arbors (mandrels) that connect them to a drill, and other accessories.
The type of saw material dictates what it can cut:
High Carbon Steel (HCS): Primarily for wood, drywall, plaster, and soft plastics. These are common in general-purpose, budget-friendly 16-piece sets.