Monospaced fonts are also known as non-proportional. Indeed, all the signs are equal in the width, as opposed to the typefaces with variable letter and symbol sizes. They were pioneered for typewriters and became widespread in computers and terminals which had limited capabilities at first.
Even today the vast majority of text redactors and development environments set Monospaced fonts as default: their convenience is irreplaceable when working with the code. In all technical manuals fixed-width fonts also prevail: the code is clearly recognizable even if text is translated.
Nevertheless, Monospaced fonts are not suitable for usual books and other types of products containing large texts due to perception problems. Examples: Courier, Lucida Console, Letter Gothic, Andale Mono, Consolas, Courier New.