There are a couple different types of fonts that have a fixed width. The most common type of fixed width font is called a monospaced font. Monospaced fonts have each character take up the same amount of horizontal space. This makes them great for code editors, terminal applications, and other applications where you want the text to line up evenly. Some popular monospaced fonts include Courier, Monaco, and Andale Mono.
There are also a few proportional fonts that have been designed specifically to have a fixed width. These fonts are less common, but they do exist. Two popular examples of fixed width fonts are SFFixed and Fira Mono.