Definicija: Na mednarodni ravni ni splošne sprejete definicije. Izraz najpogosteje označuje vse primere, ko oseba samostojno, brez vpliva drugih zunanjih dejavnikov, sprejme odločitev, da bo migrirala zaradi "osebnih ugodnosti". Ta pojem torej vključuje osebe in njihove družinske člane, ki potujejo v druge države ali območja, da si izboljšajo materialne ali socialne razmere ter nadaljnje možnosti zase in za življenje svojih družin.

Definicija: Vrnitev osebe v izvorno državo ali državo običajnega prebivališča, potem ko je vsaj eno leto preživela v drugi državi. Ta vrnitev je lahko prostovoljna ali ne. Vrnitvene migracije vključujejo tudi prostovoljno repatriacijo.

Definicija: The Advisory Committee is empowered to examine general questions or questions of principle and problems arising from the implementation of the Regulations adopted within the framework of the provisions of Article 51 of the Treaty (i.e. measures in the field of social security as are necessary to provide freedom of movement for workers) and to formulate opinions on the subject for the Administrative Commission and proposals for any revision of the Regulations.

Definicija: The Administrative Commission is responsible for tranaslation and interpretation concerning the implementation of Regulation (EEC) No 1408/71;further, it should foster and develop co-operation between Member States in social security matters with a view to expediting, it should assemble the factors to be taken into consideration for drawing up accounts relating to the costs to be borne by the institutions of the Member States under the above Regulation and to adopt the annual accounts between the said institutions, and it should undertake any other function within its competence.