Alphabetic character spacing based on the width of each letter in a font. For example, an I takes up less horizontal space than an M. Proportional spacing is commonly used for almost all text. In this encyclopedia, the default text is a proportional typeface, and tables are "monospaced," in which all characters have the same fixed width. See kerning
Proportional vs. Monospaced
In proportional spacing, the I takes up less horizontal space than the M as in the word "immersive." Note the white space before and after the I in the monospaced letters "siv."