Bremsstrahlung is the German word for 'slowing down' or 'braking', and here it is used to describe the radiation which is emitted when electrons are decelerated or "braked" when they are fired at a metal target.

Accelerated charges give off electromagnetic radiation, and when the energy of the bombarding electrons is high enough, that radiation is in the x-ray region of the electromagnetic spectrum. It is characterized by a continuous distribution of radiation called continuous x-ray spectrum which becomes more intense and shifts toward higher frequencies when the energy of the bombarding electrons is increased.

A projectile electron can lose any amount of its kinetic energy in an interaction with the nucleus of a target atom, and the bremsstrahlung radiation associated with the loss can take on a corresponding range of values.

For example, an electron with kinetic energy of 70 keV can lose all, none, or any intermediate level of that kinetic energy in a bremsstrahlung interaction; the Bremsstrahlung X-ray produced can have an energy in the range of 0 to 70 keV. Here, 70 keV is the energy that corresponds to the cut off wavelength (smallest wavelength - highest frequency therefore the highest possible energy - use E=hf=hc/l to calculate it). This is different from the production of characteristic x-rays that have specific energies.