Non-proportional font
Appearance
A font where all characters are displayed using the same width is considered a non-proportional font. For example, on a screen that is 80 characters wide, each character has a width of 1/80th of the screen. A non-proportional font is better than a proportional font for some purposes, because the characters line up in nice, neat columns.
ASCII art requires a non-proportional font for proper viewing. In a web page, non-proportional fonts are used by the <pre> tag. In LaTeX, non-proportional fonts are used by the verbatim environment.
The proportional font entry features a comparison.