Originally, a non Greek speaker whose language sounded gutteral to the "civilized" Greeks.
Historically, a nomadic people who subsided by hunting and gathering -- and raiding.
In Civ 1 terms, a civilization that can't develop Agriculture and Road-Building, the advances necessary to create Settler and therefore found a city.
In Civ 3 terms, basically the same as above, but the designers no longer mention Agriculture and Road-Building in the splash page description of the players core starting assets.
"Goody huts" sort of fill the role of minor civs that were based on agriculture but that never became a major contender as a world power (and were credited as such by historians.)
I think it would be neat-o if the Civ designers included a mechanism for Barbarian tribes to develop agriculture over time, through trade or innovation. Start the game 4000 yrs earlier and each civ would begin as one of a-100-or-so of nomadic tribes wandering around, settling pre-city villages (goody huts) as part of the process of developing agriculture. Would allow for late Civs (like the Germans) to rise to power at a later date than earlier Civs (e.g. Egyptians...)