This term refers generically to any flare model involving fast particles "precipitating" from the corona into the dense lower atmosphere. The nomenclature comes from the nature of the bremsstrahlung continuum emitted by electrons in such a particle beam; by analogy with standard laboratory X-ray sources. Electrons emit bremsstrahlung as they slow down collisionally, and the spectrum produced thus integrates over all electron energies below the initial injection energy. The alternative is a thin target, which has negligible collisional loss so that the bremsstrahlung emission comes from monoenergetic electrons. Probably the first cartoon to envision such a model, and also to make the parallel with type III radio emission, was that of Anderson & Winckler (1961),