What is it called when Japanese words are used as syllabaries?

The modern Japanese writing system is a combination of three character types: logographic kanji, which are adopted Chinese characters; syllabic kana; and in some cases the Latin script (rōmaji). Kana itself consists of a pair of syllabaries: hiragana, used primarily for native or naturalised Japanese words and grammatical elements, and katakana, used primarily 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.

Hiragana is used to write native words for which there are no kanji, including grammatical particles such as から kara "from". Likewise, hiragana is used to write words whose kanji form is obscure, not known to the writer or readers, or too formal for the writing purpose.