double-width character
Computing term for a character that occupies two standard character cells, typical of CJK characters in monospaced environments.
Japanese characters are usually treated as double-width characters.
半角文字 refers to half-width characters, typically ASCII, while 倍幅文字 refers to full-width or double-width characters.
Compound of 倍 (double), 幅 (width), and 文字 (character). A straightforward technical term.