Charity Slots

I am currently looking into registering for a race that only have charity slots available. What does this mean? The charity is not listed, I contacted the RD and was told they have not decided on a charity yet and when they do they will then post it.

This is the Augusta, GA HIM. First year race, sold out of regular spots. I don't mind doing the charity, however I am concerned it will go to a IMO a non worthy cause. My sponsor said I could do it if it was a worthy cause. How could I justify it to the sponsor?