An air filter is a device that removes impurities and pollutants from the air that passes through it. It is commonly used in heating, ventilation, and air conditioning (HVAC) systems, as well as in air purifiers and other appliances. The filter typically consists of a porous material, such as fiberglass or pleated paper, which traps particles such as dust, pollen, and mold spores as air flows through it. The effectiveness of an air filter is measured by its Minimum Efficiency Reporting Value (MERV) rating, with higher ratings indicating better filtration. Regular replacement of air filters is important for maintaining good air quality and preventing clogs that can reduce system efficiency.