Quote from FullyArticulate:
For currencies, the commercials are banks. The non-commercials are hedge funds. The non-reportables are the 21yo with Etrade accounts.
There are some gray areas that the CFTC is attempting to rework the COT to fix. For example, swaps dealers may be excessively long when true hedgers are typically short, but they're both included in the same category for different reasons.
This is a poorly formatted, but useful story on the topic:
http://www.biofuelsjournal.com/arti..._of_Traders_Report______12_06_2006-39684.html