What is 1 millionth of a meter commonly referred to as?

1 millionth of a meter is commonly referred to as a micron, which is equivalent to 1 micrometer (µm). This unit is widely used in various fields, including filtration and air quality, as it is particularly relevant for measuring particles in the air and the size of particles that various filters can capture. For context, in air filtration, understanding particle sizes in microns is essential for assessing the effectiveness of different types of filters and their ability to trap specific pollutants or allergens.

The other options represent different measurements: a nanometer is one billionth of a meter, a picometer is one trillionth of a meter, and a centimeter is one hundredth of a meter. Each of these units serves different purposes based on the scale of measurement needed, but they do not represent one millionth of a meter, which is why they are not applicable in this context.