In Japanese, the word rōmaji (ローマ字, lit. Roman characters) broadly refers to the Roman alphabet. In English, the word is usually used to refer specifically to the writing of the Japanese language in Roman characters as opposed to the usual mix of kanji and kana.
Japanese may be written in Romaji for many reasons: street signs for visiting foreigners; transcription of personal, company, or place names to be used in another language context; dictionaries and textbooks for learners of the language; or even simply for typographic emphasis.
There are a number of different romanization systems in use, including the common Hepburn and Monbusho systems.
Kunrei-shiki (訓令式; also called "monbusho" system) is a romanization system for transcribing Japanese language into the Roman alphabet. It is the system preferred by the Monbusho (Japanese ministry of education), although it is much less widespread in use than Hepburn romanization and is mostly used within Japan.