Bremsstrahlung (braking radiation) is electromagnetic radiation produced when a charged particle decelerates, when its course is deflected by another charged particle. A photon is emitted that balances the energy equation. The resulting radiation emission has a continuous spectrum (continuum emission), as opposed, for example, to emission lines. It is also called free-free radiation in expressing the point that it is not from an electron bound to an atom.
An astronomical source of bremsstrahlung is the intracluster medium associated with a galaxy clusters.
The reverse of bremsstrahlung radiation is also possible, called free-free absorption, where an electron and another particle interact and a photon is absorbed. Free-free absorption occurs in HII regions, affecting their spectrum.