Tenders are sales that use sealed bids that buyers submit directly to the seller. Once the tender ends, the seller will pick the winning bid and the winner will be notified. Unlike with auctions, buyers do not see any other bids that have been made. Buyers can submit more than one bid, but can not withdraw a bid once it has been submitted.
Auctions are sales that automatically award what's sold to the highest bidder. Buyers can submit bids for lots in the auction until the lots close, and all submitted bids are final and cannot be withdrawn. Buyers are able to see the full bidding history for all the items in the auction.