What's the difference between a serif font and a sans-serif font? A serif is a fine line that marks the end of letter's main stroke. Think of the little horizontal feet that the "m" on an M&M's candy sits on. Conversely, a sans-serif font lacks those little lines. (In French sans means "without.")
Times New Roman is the most common serif typeface, having been around for nearly a century. It was commissioned by the UK newspaper The Times from which it gets its name.
Sans-serif fonts are modernist, perceived as being "clean." The most famous sans-serif font is Helvetica which has graced everything from street signs to the logos of Apple and Target.