Microns refer to a unit of measurement used to indicate the size of particles and objects. Other synonyms for microns include micrometers, which is the scientific term for microns. Nanometers are also another synonym frequently used, and they are even smaller than microns since they measure one billionth of a meter. Another synonym is a thousandth of a millimeter, which is also known as a micrometer. Lastly, millimicrons, or nanometers, can also be used to describe quantities that measure less than a micron. They all refer to minute measurements that are too small to be measured with the naked eye.