Internet Explorer 6 is a web-browser which was released in 2001. That's 10 years ago! 10 years might not seem like a long time, but the internet has changed a lot in the last 10 years.
Internet Explorer 6 was a great web-browser in its day (and it really was much better than its predecessors!), but that day has long passed.
Last week, Microsoft launched their IE6 Countdown website: it contains some shiny graphics and information about how and why you should move away from Internet Explorer 6.
If you're still using IE6 I strongly recommend that you upgrade to a later version of Internet Explorer, or switch to another browser. Mozilla Firefox is very popular, but my preferred browser these days is Google Chrome.