Sending and receiving business documents with your trading partners becomes more efficient when your computer and theirs are communicating with each other.  Since computers don't understand as much as you and I, we have developed a common set of terms (or language) so that everyone involved, including the computers can understand just where your order is in the process.  The e-PSA Business Dictionary can be found here:

http://www.epsa-labs.com/QueryEBDE/

Once you've clicked on the link, enter a Business Dictionary Term and it will return a list of valid values for that field.  As an example, if you enter GlobalLineItemStatusCode it will return all of the available purchase order line item status codes.  Or you could see that same list by clicking here