Bremsstrahlung (Braking Radiation) is Electromagnetic Radiation (EMR) 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.
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 (HII), affecting their spectrum.
Kramers' Opacity Law