Any person or organization that donates to your auction is a Donor. Donors can be featured on the item page they donated. From there, if they “sponsored” your auction further with a cash or in-kind donation you can elevate them to be a Sponsor.
Sponsors can be featured globally on your online auction, meaning their logo will appear at the bottom of every page (home page, item pages, etc). This can be managed under Donors > Sponsorship Center. You can have unlimited global sponsors divided into up to 4 tiers.