This name was used by the Romans to refer to the region inhabited by the Britons, a Celtic people who lived in what is now Wales.
The name itself is thought to be derived from the Brittonic word "*Gwaled" meaning "foreign land" or "land of strangers" - likely used by the Romans to distinguish it from their own territory.
Over time, "Wallia" evolved into "Wales" in English. It's important to note that the Welsh language name for Wales is "Cymru," which has a different etymology and is believed to come from the name of the ancient Brythonic tribe, the Cymry.