The maximum bid, also known as proxy bids, is the highest amount you are willing to pay for an auction lot.
When you set your max bid, the auction software automatically places bids on your behalf at the next available increments if other competitive bids come in to keep you as the highest bidder up to your maximum bid and never any further.
If no one else bids higher, the max bidder wins the auction at the lowest possible price, which is the amount of the second-highest bid plus the minimum increment.
Max bids can be advantageous for bidders who can't constantly monitor an auction or who want to avoid bidding wars. By placing a max bid, they can set a limit on how much they're willing to pay and let the system do the rest.
Please also see our article on "Bidding Increments".