One of the age ratings of the Entertainment Software Ratings Board. This rating is aimed at people who are at least 18 years old. No one under 18 is permitted to buy games that are rated AO, though it is not legally binding in the United States (it is in some Canadian provinces, however). This is why it is termed "Adults Only".
You might be confused as to why the top rating is only one year above the Mature Rating. Generally, only games with pornographic content, or at least borderline porn, give a game the AO rating, and it's quite possible the highest rating was made to conform with general pornography laws, when the ESRB otherwise felt that 17 is the true developmental cutoff. However, there are a few games that have this rating solely because of their violent content.
One would think that if a game gets a lot of attention and money for being rated M, then surely rating it AO will make it sell even better, right? Not quite. Similar to an "NC-17" rating, an AO rating is a death sentence to a game's financial viability, as every large retailer will refuse to stock AO games, and the current major console makers refuse to license them due to the association of "adult-only" ratings with pornography. In addition to the above, livestreaming website Twitch has outright stated that they prohibit AO-rated games from being streamed on their site, although any M-rated versions of certain games (such as Grand Theft Auto: San Andreas and Fahrenheit: Indigo Prophecy) are still allowed.
Video Games with TV Tropes pages that have received this rating:
- Critical Point: Strong Sexual Content, Violence
- eden* PLUS+MOASIC: Nudity, Strong Language, Strong Sexual Content note
- ef - a fairy tale of the two.: Blood, Nudity, Sexual Violence, Strong Language, Strong Sexual Content note
- Fahrenheit: Indigo Prophecy - Director's Cut: Blood, Nudity, Strong Language, Strong Sexual Content, Use of Drugs and Alcohol, Violencenote
- Grand Theft Auto: San Andreas: Blood and Gore, Intense Violence, Nudity, Strong Language, Strong Sexual Content, Use of Drugs note
- Hatred: Intense Violence, Blood and Gore, Strong Language note
- Leisure Suit Larry: Magna Cum Laude Uncut and Uncensored!: Mature Humor, Nudity, Strong Language, Strong Sexual Content, Use of Alcohol
- Lula 3D: Blood, Nudity, Strong Language, Strong Sexual Content, Violence
- Manhunt 2: Blood and Gore, Intense Violence, Strong Language, Strong Sexual Content, Use of Drugs note
- Riana Rouge: Realistic Blood and Gore, Strong Sexual Themes
- Singles Flirt Up Your Life: Nudity, Strong Sexual Content (also released in an M-rated version)
- Snow Drop: Strong Sexual Content
- Thrill Kill (officially unreleased): Animated Blood and Gore, Animated Violence