I don't want technical answers

Answer:
Matt's right about plasma, it's gas that lights up when charged. But for LCD's, it's actually projection tv's that use mirrors, direct-view LCD tv's don't. They use cells of liquid crystal which sort of twist when they're charged; the twisting either grants light from the backlight through or blocks it. A more technical person might say this isn't exactly how it works but it's basically right.

I'm not sure if you want the merits of each but here are some more just in case:

-plasma traditionally does fast motion superior while LCD's have a bit of blurring (this difference is lessening especially if you get an LCD with a fast response time and a tv that can show 120 Hz (120 frames per second - for lower framerates it shows them more than once each -> improves fluidity))

-plasma can show darker blacks because individual pixels can be turned off while an LCD's backlight is always on and can leak (so absolutely black appears as very dark grey on an LCD)

-some state plasma can show more accurate colours

-LCD is imune to screen burn-in which makes it great for anything that stays onscreen for a long time like video games and tv station corner-logos (I hate those!). Plasmas have some quick-fix workarounds (like slowly moving the picture around) but they haven't solved it.

-LCDs don't usually have as much glare and appear brighter in bright rooms

-LCDs are more convenient in a few areas like: they're lighter, run cooler, use less electricity and are sturdier (less likely to be damaged when moving them).

These differences are lessening as technology improves. In my thought, both have their problems but there's not much choice for now if you want a thin HDTV (still waiting for Laser tv and OLED to improve lifespan and get a lot Cheaper!).

Answer:
plasma uses gases and LCD uses mirrors. both provide HD but plasma is more expensive in many cases. the LCD lasts long though