We need new words. The constantly changing patterns of modern life demand them. Some disappear rapidly without trace, but many find a place in the language, however briefly. They reflect the times we live in. Such terms as Sloane Ranger, yuppie, bimbo and toy boy would not have survived unless they corresponded to real people. Hip hop, rave and rap represent moments in present-day culture. Chair or chairperson, significant other and similar examples of political correctness are rapidly becoming part of the currency of everyday speech. Viruses and piracy have taken on new meanings in the computer age. Gazundering and negative equity have a special significance in recessionary times. 
Words seem to have lives of their own. Old words acquire new meanings and old meanings acquire new words. Modern developments and events have new words coined for them. Words cross frontiers and generation gaps. They start as obscure scientific terms, move to sociology or business and finally become part of popular speech. 
Here, then, is the essential guide to the meanings, and shades of meaning, of the words and phrases that can sometimes be bewildering in the speech and writing of today.