A community theatre has one donated painting and many interested buyers. Nobody knows what it will sell for. An auction lets the buyers reveal offers, then uses an announced rule to choose a winner and a price. The theatre can raise money without first guessing the right asking price.
That simple idea contains several different arrangements. In an ascending auction, bidders can respond to one another. In a sealed-bid auction, they submit offers without seeing competing bids. Auction design changes what participants learn and how they bid; the winner need not always pay the number written on their own offer.
What the bid measures
The highest bid identifies the person willing and able to pay most under those rules. It does not identify who needs the painting most, or who would give it the best home. Auctions are powerful precisely because they make one criterion decisive; they become misleading when that criterion is mistaken for every kind of value.
For the theatre, several independent bidders make the process more informative. If the only two serious buyers agree to keep their bids low, the ceremony of competition remains while much of its substance disappears. The object, information available to bidders, and opportunities for collusion all belong to the design.