Bremsstrahlung emission, from the German "braking radiation", refers to electromagnetic waves produced when a charged particle accelerates and some of its kinetic energy is converted into radiation. Thermal bremsstrahlung refers to radiation from a plasma in thermal equilibrium and is primarily driven by Coulomb collisions where an electron is deflected by the electric field of an ion. This is often referred to as free-free emission for a fully ionized plasma like the solar corona because it involves collisions of "free" particles, as opposed to electrons transitioning between bound states in an atom. This is the main source of quiescent background emission from the corona, where quiescent means outside of radio burst periods.