LCD= liquid crystal display, liquid crystals are illuminated by a florescent back light.
LED= light emitting diode, picture is produced by a series of diodes assigned to each color.
PLASMA= plasma is a mixture of gasses that are illuminated by a florescent backlight.
LED and PLASMA are heavier than LCD plasma costs more to operate and is prone to screen fade over time as the gasses break down. LCD if the florescent tube dies you're screwed, with LED if a diode dies you could loose a certain color and still have the remaining. This is what I was told from Best Buy anyhow