Japanese phonetic lettering system
Unlike Kanji, which is made up of ideograms or pictograms where the characters are abstract representations of actual objects or concepts (ie. drawings), Hiragana is a purely phonetic character set of 75 or so "letters" intended to represent a sound. Hiragana is also used for sentence particles and parts of words or phrases — any sentence of Japanese writing will have a combination of hiragana and kanji. Also, it is different from the other phonetic character set, Katakana, in that it is used for native Japanese vocabulary and loan (foreign) words introduced into Japan before the 1900's.
Here, a basic Japanese sentence where Hiragana letters are in black and blue (blue are sentence particles), Katakana letters are in green and Kanji in red: