Block: Halfwidth and Fullwidth Forms

Range U+FF00 - U+FFEF
Official Chart http://www.unicode.org/charts/PDF/UFF00.pdf
Wikipedia In CJK (Chinese, Japanese and Korean) computing, graphic characters are traditionally classed into fullwidth (in Taiwan and Hong Kong: 全形; in CJK and Japanese: 全角) and halfwidth (in Taiwan and Hong Kong: 半形; in CJK and Japanese: 半角) characters. With fixed-width fonts, a halfwidth character occupies half the width of a fullwidth character, hence the name. In the days of computer terminals and text mode computing, characters were normally laid out in a grid, often 80 columns by 24 or 25 lines.
https://en.wikipedia.org/wiki/Halfwidth_and_Fullwidth_Forms_(Unicode_block)
Characters
_ ソ ﾿