Noun
(US, film) a movie that is intentionally written to be R-rated ("Under 17 requires accompanying parent or adult guardian.") by the Motion Picture Association (MPA), typically due to having multiple scenes of violence or nudity.
Alternative letter-case form of hard r.
(phonetics, phonology, informal) a rhotic sound which is emphatic or strongly enunciated; in English accents especially a postvocalic consonantal r, as distinguished from its absence in a nonrhotic accent or from an R-coloured vowel
(US, in particular), the hard r at the end of the word nigger when spoken with a General American accent and considered maximally racist; as distinct from the African-American Vernacular English pronunciation conventionally spelled nigga, whose final sound is sometimes called soft a
Source: en.wiktionary.orghard-R