The 5 font families

Since not all fonts are available on all computers (there are thousands of fonts, and most are not free), CSS provides a system of fallbacks. You list the font that you want first, then any fonts that might fill in for the first if it is unavailable, and you should end the list with a generic font, of which there are five: serif, sans-serif, monospace, cursive and fantasy.

It is best to specify type faces in groups since different computers use different type fonts:

font-family: font family: Verdana, Arial, Helvetica, Geneva, SunSans-Regular, sans-serif
'sans-serif': normal fonts without serifs

font-family: Georgia, "Times New Roman",Times, serif
(Times New Roman is the default for most browsers)
'serif': normal fonts with serifs

font-family: "Courier New", Courier , monospace
'monospace': fixed-width fonts

font-family: Zapfino, Zapf Chancery, cursive
'cursive': fonts that emulate handwriting

font-family: Papyrus, Impact , fantasy
'fantasy': decorative fonts, for titles, etc.

For more on fonts : http://www.wpdfd.com/editorial/wpd0704news.htm