Was it emailed to you or did it show up on your ebay page once you were logged in? or is it a code someone else has shared??
The reason I say this is sometimes ebay sends tailored discounts to various members for different reasons, and to use in different selected departments
I recently received a £10 off code that could be used on anything, giving me 5 pairs of reading glasses for the grand total of 48p
EDIT: never mind, it appears to be a fully working code this could be very dangerous for me!!