With the introduction of foreign words increasing every year, the use of katakana only expands with time. Even seasoned students of Japanese should brush up on their characters once in a while.
Katakana (片仮名, カタカナ or かたかな?) is one of two Japanese syllabary, one component of the Japanese writing system along with hiragana, kanji, and the Latin script romaji. Katakana itself means "fragmentary kana", as they are unique characters derived from simplifying more complex Chinese characters. Katakana and hiragana are both called "kana"; for ever hiragana character, there is an equivelent katakana character, and each one represents one "mora" (a discrete sound in the Japanese language). Each kana is either a vowel, such as "e" (katakana エ); a consonant and vowel combination like "ha" (katakana ハ); or "n" (katakana ン). There is also a nasal sonorant that can sound like an English n, m, or ng ([ŋ]), much like the nasal vowels of Portuguese or French.
Where katakana is distinct from hiragana syllabary, katakana is used to sound out foreign loan words imported into usage amongst the Japanese when those words are written down. Foreign loan words are collectively known as gairaigo. Secondly, it is also used for particular emphasis, to represent frequently used onomatopoeia phrases, and also to write certain native Japanese words, like scientific terms, or names of animals, plants and minerals. Names of Japanese companies often also appear written in katakana rather than the other systems.
Katakana consists of 48 characters:
5 singular vowels characters
42 distinct consonant-vowel pairs, consisting of 9 consonants paired with each of the 5 vowels, of which three combinations (yi, ye, wu) are not used.