Bidding on searches for a brand's own name, by the brand itself or by anyone else: resellers, competitors and affiliates.
Brand bidding means showing search ads on searches for a brand's name: “yourbrand”, “yourbrand sale”, “yourbrand discount code”. The brand usually does it itself, in a brand campaign. Others can too. Google's Trademarks policy doesn't restrict trade marks used as keywords, so a reseller, a competitor or a publisher can bid on your name, and a trade mark complaint reaches only the words in their ads.
For an affiliate programme, it's a question for the programme terms. Many rule it out for publishers without written permission, covering the name, its misspellings and the name with other words. Some allow it for named partners. Google's Unfair advantage policy lists affiliates who advertise on Google Ads against their programme's rules as something it doesn't allow.
- “Bid on” covers the keywords a publisher chooses. “Appear on” covers every search Google matches them to, close variants included.
- Negative keywords are how a publisher allowed on generic searches stays off yours.
- Auction insights shows who else took part in your brand campaign's auctions, by display domain.
The guide to who's bidding on your brand shows how to find them, and whether to bid on your own name has a guide of its own.
Google's own help and policy pages first.