MERV, or Minimum Efficiency Reporting Value, measures how well air filters catch airborne particles. Higher MERV ratings mean the filter traps smaller particles like dust and pollen better. A MERV rating of 6-8 is usually a good choice for most homes, balancing filtration and airflow. If you have allergies or respiratory problems, a higher MERV rating can help, but be sure your furnace can handle the filter's airflow restriction.