Definition of hard r:
(n) :
(US, film) A movie that is intentionally produced to be R-rated ("Under 17 requires accompanying parent or adult guardian") by the Motion Picture Association (MPA), typically due to its multiple scenes of violence or nudity.
(n) :
(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.
(n) :
(chiefly US) The hard r at the end of the word nigger when spoken with a General American accent and considered more offensive than the African-American Vernacular English pronunciation conventionally spelled nigga, whose final sound is sometimes called soft a.
(n) :
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.]