OpenWindows Advanced User's Guide Fixed-Width and Proportionally-Spaced Fonts

Note that there are two general categories of fonts--fixed-width and proportionally-spaced. Each character in a fixed-width font takes up the same amount of space as every other character. By contrast, the characters in a proportionally-spaced font require varying amounts of space, depending upon their individual width. Proportionally-spaced fonts are more pleasing to the eye. However, some applications (such as Command Tool, Shell Tool, and xterm, a popular terminal emulator application) work best with fixed-width fonts.