A Brand BOT is an automated crawler or ROBOT that visits websites usually when links to a site are posted on Twitter to see whether the "Brand" is mentioned within the posted webpage.
These Brand BOTS make up a large majority of BOTS that visit a site during a Twitter Rush and do nothing to benefit the site in question. They usually just overload the sites server, often causing a slow down that effects the speed of a loading webpage.
Stupid Brand BOTS took my site down during a Twitter Rush when I posted that link to my new blog article in a Tweet.
I am going to fill my .htaccess file up with every Brand BOT I can find and ban them from visiting my site.