A question similar to this came up in a forum recently, essentially the question was "Where can you change the description of a transaction from a Dynamics GP Receivings Shipment or Shipment/Invoice"?

The short answer is, that it's very well hidden but it is there, and most users don't see it and generally, it stays at the default value which is "Receivings Transaction Entry". That means if you print transaction descriptions on an Accounts Payable cheque or EFT remittance, that's what you see.

Here is a view of a posted journal entry reference field, the source you can see is RECVG, and the default description "Receivings Transaction Entry" appears if the user does not change it during entry:

The Transaction Entry Zoom window showing the reference has the default description from a Receivings Transaction posting.
The Transaction Entry Zoom window showing the reference has the default description from a Receivings Transaction posting.

Here is where the field comes from, in Receivings Transaction Entry:

The Purchasing Distribution Entry window where the Reference field comes from, showing I've typed in "Phone purchases" in the field.
The Purchasing Distribution Entry window is where the Reference field comes from.

And here is what shows when posted:

The Purchasing Distribution Entry window where the Reference field comes from.
The Journal Entry Inquiry window after posting shows the Reference matches what I had in my transaction entry in the previous screenshot, "Phone purchases".

Hopefully this helps those who have been looking for where to change this description!