Plasma frequency is the natural oscillation frequency of electrons in a plasma, which is a state of matter consisting of charged particles. It is determined by the density of the electrons and is crucial for understanding how plasmas interact with electromagnetic waves. When the frequency of an incoming wave is lower than the plasma frequency, the wave cannot propagate through the plasma. In astrophysics, plasma frequency plays a significant role in the behavior of cosmic plasmas, such as those found in stars and galaxies. It helps explain phenomena like radio wave propagation in space and the dynamics of solar winds, influencing how these charged particles interact with magnetic fields.