Gambling sites are sites that have gambling as their central theme. If the site meets these criteria, the advertiser may bid only on search terms that are plainly associated with gambling (e.g. "poker" or "roulette") or that contain an explicit gambling modifier (e.g. "fa cup odds").
In the UK, gambling sites are defined around games of chance, as opposed to games of skill. This includes sites that accept wagers or require payment in exchange for the chance to win prizes.
"Fantasy football" sites and sites that offer prizes for skilled competition are not considered to be gambling sites.