A figure space is a typographic unit equal to the size of a single typographic figure (numeral or letter), minus leading. Its size can fluctuate somewhat depending on which font is being used. This is the preferred space to use in numbers. It has the same width as a digit and keeps the number together for the purpose of line breaking.
Standard
In Unicode it is assigned U+2007 FIGURE SPACE (HTML  ).
Baudot code may include a figure space. It is character 23 on the Hughes telegraph typewheel.
References
Figure space Wikipedia(Text) CC BY-SA