Which unit of measurement is denoted by the symbol 'μm'?

The symbol 'μm' denotes a micron, which is a metric unit of measurement equal to one-millionth of a meter, or 10^-6 meters. Microns are commonly used in various scientific and technical fields, including biology and materials science, to measure extremely small distances, such as the size of microorganisms, particles, and fibers. This unit is particularly relevant in the field of wastewater treatment, where understanding particle sizes can be crucial to processes like filtration and sedimentation.

The other units mentioned are significantly larger in scale or different types of measurements. For instance, a millimeter is one-thousandth of a meter, a microliter is a unit of volume equivalent to one-millionth of a liter, and a mile is a unit of distance typically used in the imperial system, equivalent to 1,609.34 meters. The micron's specific application in measuring very small dimensions sets it apart from these other units.