The rules for using kana (phonetic syllabary) in writing — i.e., kana orthography. Distinctions include modern and historical kana usage.
古文を読むときは昔の仮名遣いに慣れておくと便利だ。
It's useful to be familiar with historical kana orthography when reading classical texts.
作文の課題は新しい仮名遣いに従って書いてください。
Please write the composition according to the modern kana orthography.
学校で仮名遣いの基本ルールを習った。
I learned the basic rules of kana orthography at school.