Dust Mask.

It is designed to protect the wearer from inhaling harmful dusts, fumes, vapors, or gases. This specific dust mask appears to be a reusable type with a blue plastic frame and replaceable filters. They are commonly used in various settings like construction, woodworking, and general DIY tasks to filter out dust, pollen, and airborne particles. It's important to note that dust masks like this are generally for non-toxic nuisance dusts and may not offer protection against hazardous substances or be a substitute for NIOSH-approved respirators.