Brand bidding is when an affiliate targets specific keywords associated with a merchant. This can also be a noun or adjective that describes the product. Usually when brand bidding, an affiliate is bidding on a trademarked name, and is often therefore competing directly with the merchant.
Your policies on brand bidding need to be clearly indicated in your merchant Terms & Conditions. The Commission Factory dashboard allows you to place restrictions on keywords that you want protected. Do this via the "campaign" setting in your merchant profile area, and enter the keywords that you want to restrict in the given area.
Some merchants allow brand bidding to increase visibility on a more consistent basis. You may also choose to allow affiliates to use your brand name, limiting their usage to markets or search engines where you are not active.