A weak line in the same energy region as a normal X-ray line. Another name used for weak features is non-diagram line. Recommendations as to the use of these two terms have conflicted. Using the term @D01664@ as defined here, non-diagram line may well be used for all lines with a different origin. The majority of these lines originate form the dipole-allowed de-excitation of multiply ionized or excited states, and are called multiple-@I03183@ satellites. A line where the initial state has two vacencies in the same shell, notably the K-shell, is called a hypersatellite. Other mechanisms leading to weak spectral features in X-ray emission are, e.g. @R05341@, the radiative @A00520@, magnetic dipole and electric quadrupole transitions and, in metals, plasmon excitation. Atoms with open electron shells, i.e. transition metals, lanthanides and actinides, show a splitting of certain X-ray lines due to the electron interaction involving this open shell. Structures originating in all these ways as well as structures in the @V06589@ of molecules and solid chemical compounds have in the past been given satellite designations.