November 20, 2012 4:20:30 PM MST
Reserve Auction sets a minimum price below which the seller is not obliged to sell the property at auction expiry.
The reserve price is also usually undisclosed. However when the reserve price is met, the seller would indicate that the reserve price has been reached so that bidders know that the property will now sell for sure, to the highest bidder recorded by the auction expiry date/time.
More details.