Dispersion measure (DM) is a term used primarily in astronomy to quantify the amount of dispersion a radio or electromagnetic wave experiences as it passes through an ionized medium, typically interstellar or intergalactic space. This measure arises from the dispersion caused by the free electrons present in these regions, where lower-frequency waves travel slightly slower than higher-frequency waves due to their interactions with the electrons. DM is quantified as the integrated column density of free electrons along the line of sight from the source to the observer and is typically measured in parsecs per cubic centimeter (pc/cm³) or in equivalent units. Astronomers use DM to study and understand the density and distribution of ionized material in space, aiding in the exploration of cosmic phenomena such as pulsars, fast radio bursts, and interstellar medium characteristics.