Wikipedia
Barbaricum is a geographical name used by historical and archaeological experts to refer to the vast area of barbarian-occupied territory that lay, in Roman times, beyond the frontiers or limes of the Roman Empire in North, Central and South Eastern Europe. In the Late Antiquity it was the Latin name for those tribal territories not occupied by Rome that lay beyond the Rhine and Danube (but not for Persia): Ammianus Marcellinus used it, as did Eutropius The earliest recorded mention appears to date to the early 3rd century.
In the research literature, the terms 'Germania' (which actually means Germania Magna) and 'Barbaricum' are sometimes used interchangeably, but they are not entirely identical either in the chronological or in the geographical sense. The extra-Roman area described as Barbaricum was, from the beginning of the Migration Period, not exclusively inhabited by Germanii, even though they represented the majority of the population until the time of Late Antiquity. In the Migration Period, Alans and Huns also pushed forward into this area before and, later (from the 6th century), Slavic tribes populated the area east of the Albis ( River Elbe) that the Germanii had largely abandoned.
It is important to highlight the diverse cultural, social and economic contacts between (Germanic) Barbaricum and the Empire since the early imperial period. Archaeologically, numerous imported Roman artefacts have been uncovered among the finds in the Barbaricum region. The formation of major Germanic tribal units such as the Alemanni and Franks, from the time of the imperial crisis of the 3rd century was probably influenced by contact with the Roman world. Likewise, "barbarians" were able to have careers in the Roman Army.