LED is an industry acronym for Light Emitting Diode. These are usually small little “bulbs” that glow in different colors (though usually red, blue, green or orange, all of which are problems to color blind people) when they are “turned on” (conduct current as a diode).

That's also a generic term used for the lighted display on calculators and other numeric displays; they are made up of 7 distinct straight line “bar” diodes that when turned on display light in a “portion of a line” (instead of a dot) pattern. The pattern combinations can be turned on or off (does not conduct current) to form numbers or in some cases, alphanumeric characters. Some of these had an 8th “light” which was a decimal.

LCDs emulate this pattern style, though they are NOT diodes. The first to use the style was the “nixie” tube from the early 50's. The pattern is still in use today, though nixies have gone to the vacuum tube graveyard.