Collisionless shocks are shock waves that occur in a plasma medium where collisions between particles are rare or absent. These shocks are commonly found in astrophysical environments, such as in the solar wind, supernova remnants, and accretion disks around black holes. They are also observed in laboratory experiments using high-energy particle accelerators. Collisionless shocks are typically formed when a fast-moving body, such as a high-speed solar wind stream, interacts with a slower-moving medium, such as the interstellar medium. As a result of this interaction, particles are accelerated to high energies and the plasma is heated and compressed, leading to the formation of a shock wave. Research in collisionless shocks focuses on understanding the fundamental physics of these phenomena, including the mechanisms of particle acceleration, magnetic field amplification, and energy dissipation. Scientists use a combination of theoretical models, numerical simulations, and observational data to study collisionless shocks and their effects on the surrounding medium. This research is important for gaining insights into the processes that drive high-energy astrophysical phenomena and for improving our understanding of plasma physics in general.