Genkō yōshi (原稿用紙, "manuscript paper") is a type of Japanese paper used for writing. It is printed with squares, typically 200 or 400 per sheet, each square designed to accommodate a single Japanese character or punctuation mark. Genkō yōshi may be used with any type of writing instrument (pencil, pen or ink brush), and with or without a shitajiki (protective "under-sheet").
Looking up initially so I can buy some proper paper for practicing Hiragana, Katakana, and Kanji.
It’s also often spelled as genkoyoushi in Romaji.