OEM vs. non-OEM Office 2003

I’m looking to purchase ‘MS Office Professional 2003’ and I went on ‘Ebay’ saw sellers selling Office 2003 either as a ‘OEM’ product or a ‘non-OEM’ product. What is the difference in the two items?? I just want it for my home pc. The sellers with the ‘OEM’ office stated that on the COA, it was a legitimate ‘OEM’ product in bold print, and had to send a non-peripheal with the sale to meet Ebay/Microsoft rules/EULA. Another seller said he had ‘Office 2003’ for sale and that there was no ‘OEM’ stamp/print on the ‘COA’. Help, and many thanks.