Sites displaying Google ads may not include:
* Violent content, racial intolerance, or advocacy against any individual, group, or organization
* Pornography, adult, or mature content
* Hacking/cracking content
* Illicit drugs and drug paraphernalia
* Excessive profanity
* Gambling or casino-related content
* Content regarding programs which compensate users for clicking on ads or offers, performing searches, surfing websites, or reading emails
* Excessive, repetitive, or irrelevant keywords in the content or code of web pages
* Deceptive or manipulative content or construction to improve your site's search engine ranking, e.g., your site's PageRank
* Sales or promotion of weapons or ammunition (e.g., firearms, fighting knives, stun guns)
* Sales or promotion of beer or hard alcohol
* Sales or promotion of tobacco or tobacco-related products
* Sales or promotion of prescription drugs
* Sales or promotion of products that are replicas or imitations of designer goods
* Sales or distribution of term papers or student essays
* Any other content that is illegal, promotes illegal activity, or infringes on the legal rights of others
Although you do see sites with adverts on them, poker strategy seems to be allowed for example.
Depending on the nature of your site it's worth contacting them and asking.