Difference between DIV and SPAN tags

http://webdesign.about.com/od/htmltags/a/aa011000a.htm

The primary difference between the <span> and <div> tags is that <span> doesn't do any formatting of it's own. The <div> tag acts includes a paragraph break, because it is defining a logical division in the document. The <span> tag simply tells the browser to apply the style rules to whatever is within the <span>