Hiragana and katakana are both kana systems; they have corresponding character sets in which each kana, or character, represents one mora (one sound in the Japanese language). Each kana is either a vowel such as "a" (hiragana あ); a consonant followed by a vowel such as "ka" (hiragana か); or "n" (hiragana ん), a nasal sonorant which, depending on the context, sounds either like English m, n, or ng ([ŋ]), or like the nasal vowels of French. Because the characters of the kana do not represent single consonants (except in the case of ん "n"), the kana are referred to as syllabaries and not alphabets.
The modern Japanese writing system is a combination of two character types: logographic Kanji, adopted from Chinese characters, and syllabic Kana. Kana itself consists of a pair of syllabaries: Hiragana, used for native or naturalised Japanese words and grammatical elements, and Katakana, used for foreign words and names, loanwords, onomatopoeia, scientific names, and sometimes for emphasis. Almost all Japanese sentences contain a mixture of kanji and kana. Because of this mixture of scripts, in addition to a large inventory of kanji characters, the Japanese writing system is often considered to be the most complicated in use anywhere in the world.
Several thousand kanji characters are in regular use. Each character has an intrinsic meaning (or range of meanings), and most have more than one pronunciation, the choice of which depends on context. The hiragana and katakana syllabaries also originally derive from Chinese characters, but have been simplified and modified to such an extent that the character origins are no longer obvious. In modern Japanese, each contains 46 basic characters, or 71 including diacritics. Each different sound in the Japanese language (that is, each different syllable, strictly each mora) is represented by one character in each syllabary. Unlike kanji, these characters intrinsically represent sounds only; they convey meaning only as part of words.
To a lesser extent, modern written Japanese also uses acronyms from the Latin alphabet, for example in terms such as "BC/AD", "a.m./p.m.", "FBI", and "CD". Romanized Japanese, called rōmaji, is frequently used by foreign students of Japanese who have not yet mastered the three main scripts, and by native speakers for computer input.