What is "salassi"

The Salassi were a Celtic or Celticized Italic or Ligurian tribe whose lands lay on the Italian side of the Little St Bernard Pass across the Graian Alps to Lyons, and the Great St Bernard Pass over the Pennine Alps. The Romans finally defeated and enslaved many of them in 25 BCE, and founded the city of Augusta Praetoria Salassorum, modern Aosta, in their territory.