The nature of the migrating species and the overall charge state are related topics that need to be discussed. Is the migrating species in solid electrolytes really an ion or rather an atom? We will address this issue by discussing various charge partition schemes which are supposed to determine the charge state of atoms in a chemical environment. A basic notion of macroscopic materials is that they are typically charge-neutral. This concept is well-known from liquid electrolytes where the charge of any solvated ion is compensated by a corresponding counter ion. Solid electrolytes are often coined "single-ion conductor". If these materials are single ion conductors, the natural question arises: What is counter ion in these single ion materials? Furthermore, ion mobility might not just proceed via the hopping of single ions, there might be also concerted processes involved in these processes.