Baltic Dry Index (thing)
The Baltic Dry Index is a shipping cost index for major sea routes. A company in London, the Baltic Exchange, regularly calls various bulk shippers and requests price quotes for shipping cargo such as a dry commodity or a quantity of liquid from one port to another, between various ports around the world. The price quotes are used to produce the Baltic Dry Index (BDI).
The BDI is an economic indicator because it's an index of global demand for raw materials.
The index includes information for various sizes of ship, including categories called Capesize, SuezMax, Panamax and Handymax.
Capesize ships are very large and do not fit through the Panama canal, and some not through the Suez canal. The biggest ships go around the Cape of Good Hope (South Africa) or Cape Horn (South America). A Suezmax is a large vessel, but not so large that it can't go through the Suez canal. A Panamax, although smaller than a Suezmax, is still a large vessel, but not so large that it won't fit through the Panama canal. A Handymax is smaller than a Panamax.
If this is interesting, look at a chart here.