noun
18+ only; R-18; adults only
Indicates content or products restricted to those 18 years or older, similar to an age rating. Common in media, games, and online platforms.
このゲームは１８禁だから、子どもには買えない。
This game is 18+ only, so I can't buy it for children.
サイトに１８禁のマークが表示された。
An 18+ only mark was displayed on the site.
R-18 is the English-derived rating term, while １８禁 is the Japanese abbreviation for '18禁' (18 prohibited). Both mean the same but １８禁 is more colloquial in Japanese.
Abbreviation of 十八 (18) and 禁止 (prohibition), literally '18 prohibited'. A modern coinage for age restriction labeling.