noun which may take the genitive case particle 'no', noun
X-rated; adult content
Used to label media (films, games, etc.) as containing adult content, similar to an X rating. Often used attributively with の.
See also: １８禁 (じゅうはちきん)
この映画はＸ指定なので、18歳未満は見られません。
This movie is X-rated, so those under 18 cannot watch it.
Ｘ指定のゲームを買うときは年齢確認があります。
When buying an X-rated game, there is an age check.
１８禁 (18禁) means 'prohibited for those under 18' and is a broader term for adult content, while Ｘ指定 specifically refers to an X rating classification.
Compound of Ｘ (エックス, from English 'X') and 指定 (してい, 'designation'). The 'X' refers to the X rating used in film classification systems.