The span tag delimits an arbitrary piece of text. You can apply styles to the span of text. In many cases it's more convenient to use one of the predefined spans (b, i, o, u, strike, tt, zapf, symbol or nobr), but the span tag gives more flexibility, especially when given a class attribute and used with a CSS stylesheet.
<span font-family="Helvetica" font-style="italic outline"> This is in outlined Helvetica Italic </span>