Kana (かな in Hiragana, カナ in Katakana, 仮名 in Kanji, the term as used in English is both singular and plural) are Japanese phonetic characters. They come in two types: hiragana and katakana. The term is derived from the word karina meaning "provisional character".
As well as Romaji, Kana is quite frequently used for transliteration, a method to express one language in the alphabet of another language. Given that, kana is regarded as alphabet in Japanese. For example, the United States President George W. Bush can be represented in Japanese using kana like ジョージ・W・ブッシュ (Note: Japanese convention is generally to leave middle initials in alphabetic characters.)
Kana are traditionally said to have been invented by the Buddhist priest Kukai in the 9th century. Kukai certainly imported the Siddham script on his return from China in 806 CE, and his interest in the sacred aspects of speech and writing lead him to conclude that Japanese would be better represented by a phonetic alphabet, than by the Chinese Kanji or pictograms which had been used up to that point.