The Caravan arc is one of the arcs of development of Dwarf Fortress. This arc is primarily focused on fleshing out trade and the economy in both dwarf and the world as a whole.
The initial release was 0.31.19, which began to simulate food usage and trade in world gen, and added new trade goods and skills in dwarf mode.
Dwarf Fortress Consolidated Development
While outdated, Toady has explained what to expect from this arc:
As a prelude to armies, we'll have caravans actually move around the world map rather than just appear at your outpost. They'll move between each city on the map, though we'll try to stay away from supporting a real economy for the time being. You should be able to find items you traded in your fortress in adventure mode, and a caravan could come to your fortress with an adventure mode item.