Chart from ZeroHedge:
Most directly, the index measures the demand for shipping capacity versus the supply of dry bulk carriers. The demand for shipping varies with the amount of cargo that is being traded or moved in various markets (supply and demand)…
The index indirectly measures global supply and demand for the commodities shipped aboard dry bulk carriers, such as building materials, coal, metallic ores, and grains.
Because dry bulk primarily consists of materials that function as raw material inputs to the production of intermediate or finished goods, such as concrete, electricity, steel, and food; the index is also seen as an efficient economic indicator of future economic growth and production. The BDI is termed a leading economic indicator because it predicts future economic activity.