A continuum emission is an emission of electromagnetic radiation producing a range of wavelengths rather than a spectral line, i.e., a continuous spectrum. Black-body radiation is a ubiquitous mechanism. Others:
Two-photon emission is relaxation of atomic excitation producing two photons instead of one. It happens when quantum-mechanical rules forbid the normal single-photon emission and when frequent collisions are not inducing the relaxation, specifically in low-density ionized gas.