hard r

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.

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.