X-rated

First recorded in 1970–75; X³ (def. 8) + rate¹ + -ed²

The Motion Picture Association of America (MPAA) established the modern system of film ratings in the 1960s with ratings from G (for a General audience of all ages) to X (applied to films with content only suitable for adults). Many award-winning films from Midnight Cowboy to Last Tango in Paris were rated X.
In the 1960s and 1970s, pornographic films like Deep Throat were also professionally produced, shot on film, and shown in mainstream movie theaters. They were given the official rating of X. However, in the 1980s, VHS made porn production and distribution cheaper, and flooded the market with poorly produced unrated films that gave themselves the label X. The MPAA had not trademarked the X rating, and could not control the way the pornography industry coopted it.
Mainstream theaters began refusing to show X-rated movies. The producers and directors of X-rated films of that era, like Scarface , were pressured by studio executives to cut enough content to qualify for a simple R (Restricted) rating. In 1990 the MPAA replaced the X rating with NC-17, a trademarked designation for films only appropriate for adult audiences.
The X rating continued to evolve in unregulated use. If a single X indicated pornography, then more X’s must be even more pornographic. The two most common designations became X for pornography and XXX for hard-core pornography. Other common variations are XX and XXXX. In the age of the internet, many pornographic videos add three, four, or many more X’s to their titles to promote their visibility in online searches, though the X designations are not official, and their meanings can vary widely.