noun
successful bidder; tender winner; contract awardee
Refers to the person or entity that wins a bid in an auction, competitive tender, or procurement process.
オークションの落札者が発表された。
The successful bidder of the auction was announced.
公共工事の落札者は大手建設会社だった。
The contract awardee for the public works project was a major construction company.
入札者 is a bidder (anyone who submits a bid), while 落札者 is specifically the winning bidder.
Compound of 落札 (winning a bid) + 者 (person). The term is transparently derived from its components.