noun
half-width characters; single-byte characters
Refers to characters that occupy half the width of a full-width character, such as ASCII letters, digits, and katakana. Commonly used in computing and text formatting contexts. The term 'en quad' is a typographic equivalent but rarely used in everyday Japanese.
See also: 全角
パスワードは半角英数字で入力してください。
Please enter your password using half-width alphanumeric characters.
このフォームでは半角カタカナは使えません。
Half-width katakana cannot be used in this form.