LED and LCD both use an LCD display panel.
The difference is the type of light source used to provide the 'backlight' for the LCD.
(Note it's called a 'backlight' whether the actual light source is at the edge or back of the LCD panel; an optical system transfers the illumination to behind the LCD in any case).
Conventional LCD TVs use slimline fluorescent tubes, LED TVs use LEDs. There are still different designs of LED TV, with some the light source is white LEDs at the edge of the screen, while others may use white LEDs behind the screen, or even arrays of RGB LEDs behind the screen so the illumination colours can be varied over areas of the screen to emphasise the colours the LCD section is showing.
A LED backlight is likely to have a longer life than conventional LCD.
Also, as it is a newer technology, it probably means the overall TV design is newer and could be better performance.
To clarify, actual LED graphic or video displays do exists (commonly called OLED displays) - but the biggest of these are still relatively small, more like mobile phone size & definitely not anywhere near normal TV sizes.
See the link for more info: