In typography, a sans-serif or sans serif typeface is one that does not have the small features called "serifs" at the end of strokes. The term comes from the French word sans, meaning "without".
In print, sans-serif fonts are more typically used for headlines than for body text. The conventional wisdom is serifs help guide the eye along the lines in large blocks of text. Sans-serifs, however, have acquired considerable acceptance for body text in Europe.
Sans-serif fonts have become the de facto standard for body text on-screen, especially online. This is partly because interlaced displays may show twittering on the fine details of the horizontal serifs. However, the resolution of digital displays in general can make fine details like serifs disappear or appear too large.
Before the term "sans-serif" became standard in English typography, a number of other terms had been used. One of these outmoded terms for sans serif was gothic, which is still used in East Asian typography and sometimes seen in font names like Century Gothic.
Sans-serif fonts are sometimes, especially in older documents, used as a device for emphasis, due to their typically blacker type color. Read more about sans serif fonts on Wikipedia.