There may be times when the lists you have seen so far are not enough. It will fall back on its default font, unless the author provides a generic family name to provide additional fallback. This final entry directs the browser to use any available Sans-serif font if it cannot find a match for the listed fonts. There are five generic font families, although two of them are not particularly useful. The letters of Sans-serif fonts have no serifs.
Courier is the most commonly used monospace font.
Note that monospace fonts can also be either Serif or Sans-serif. Courier is a Serif font, for example. Cursive fonts are typically quite difficult to read on-screen, and their use is generally discouraged. Some browsers cannot even find and use cursive fonts. It is possible to provide a generic family which does not match the specific fonts listed, but this is not recommended.