Fullwidth form

Halfwidth and Fullwidth Forms
Range	U+FF00..U+FFEF (240 code points)
Plane	BMP
Scripts	Hangul (52 char.) Katakana (55 char.) Latin (52 char.) Common (66 char.)
Symbol sets	Variant width characters
Assigned	225 code points
Unused	15 reserved code points
Unicode version history
1.0.0	216 (+216)
1.0.1	223 (+7)
3.2	225 (+2)
Note:

In CJK (Chinese, Japanese and Korean) computing, graphic characters are traditionally classed into fullwidth (in Taiwan and Hong Kong: ; in CJK and Japanese: ) and halfwidth (in Taiwan and Hong Kong: ; in CJK and Japanese: ) 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. Each character was displayed as a small dot matrix, often about 8 pixels wide, and an SBCS (single byte character set) was generally used to encode characters of western languages.

For a number of practical and aesthetic reasons, Han characters would need to be twice as wide as these fixed-width SBCS characters. These "fullwidth characters" were typically encoded in a DBCS (double byte character set), although less common systems used other variable-width character sets that used more bytes per character.

Halfwidth and Fullwidth Forms is also the name of a Unicode block U+FF00–FFEF.

In Unicode, if a certain grapheme can be represented as either a fullwidth character or a halfwidth character, it is said to have both a fullwidth form and a halfwidth form.

Halfwidth and Fullwidth Forms is the name of Unicode block U+FF00–FFEF, the last of the Basic Multilingual Plane excepting the short Specials block at U+FFF0–FFFF.

...
Wikipedia