Tom - It's a difference in backlighting. "LED TVs" are really just LCD TVs that use LEDs for backlighting instead of fluorescent lighting.
Here's a pretty good explanation of the pros and cons:
http://www.lcdtvbuyingguide.com/hdtv/led-vs-lcd.html
We bought a Samsung LED TV about 2 years ago and couldn't be happier with it...............other than what we paid for it then versus what the same thing would probably cost today! Such is life........and the (lower) price of technological advancement!!
Hope that helps!
Bill