High energy density plasma physics is a subfield of physics that investigates matter under extreme conditions characterized by very high energy densities, typically involving ionized gases (plasmas) at high temperatures and pressures. This field explores the fundamental physical processes occurring in these states, such as radiation-matter interaction, hydrodynamics, and nuclear reactions. These conditions, often transiently created in laboratories or found in astrophysical environments like stellar interiors, are studied to advance understanding of fundamental physics under extreme states and support research into areas like inertial confinement fusion and astrophysics.