Dialects of English that drop their r's after vowels are said to be non-rhotic, as opposed to rhotic dialects.
The term comes from the negator non, from Latin, and from the Greek letter rho (transliterated as a 'r'; it looks p-like).
Australian, New Zealandish, South African, some British, and some north-eastern and southern USA dialects of English are non-rhotic.