Robots are little programs that post forum spam. Usually things that push vitamins, hair care products, etc... If they actually manage to get a post on to the fourms it's quicklyy deleted. Also referred to as bots or spambots.
Thousands upon thousands. I know, I used to run the forums for the WildCards. It's non-stop hammering of the site. Fortunately only a few get through and that's manageable.