The minimum bid increment determines the minimum amounts that your donors can submit bids in for your silent auction.
For example, if your minimum bid increment is set for $10, each bid submitted by a donor must be $10 higher than the previous bid.
You can specify a default value for all items on the Auction Settings page.
You can also override the Default Bid Increment for any item by expanding the item on the Add Items page. If you leave the bid increment blank or enter a zero the default value from the Auction Settings page will be used.