Monospaced typeface

In a monospaced typeface, every character takes up the same width. A narrow i gets as much space as a wide W, just like on a typewriter.
Most typefaces are proportional instead: each letter gets the width it needs, which makes long text flow more naturally.
Equal widths keep characters in neat columns, so monospaced type is the standard for code, tables of numbers and terminal screens. Courier and Space Mono are well-known examples.