we have seen HD TV HDDVD HD stands for High Definition. Have you ever heard of HD imagery!!
If you really want to know what High Definition means don't just Visit Wiki, give a visit to this site
Amazing "High Definition" images, When i say HD images i really mean HIGH DEFINITION
some of them are whooping 8.9GPIX in short its 149.307 x 65.984 image :)
A Picture speaks a Thousand words. in this case it surely speaks a 10^9 words ;)
My favorite HD pic is "THE LAST SUPPER IN DETAIL"
Take a look at how these images are captured