EDI and the Internet

[Robbie Honerkamp <robbie@shorty.com>]

Can anyone tell me more about EDI or do you know anyone
who can? I need a good definition of what it is (it appears to
be a set of protocols for trading items or money between companies)
and how it can be implemented in a network. I've seen mention 
of ISPs "supporting EDI" or becoming "the first EDI-enabled ISP
in the country", but I don't know what an ISP needs to do to be
EDI-enabled and why EDI software wouldn't work with any ISP.    
Also who uses it and why is it important?

Any clues/help/enlightenment would be appreciated.

Thanks,
Robbie