LED means two genuinely different things in signage, and conflating them causes most of the confusion in specifications.
The first is the backlight. Nearly every "LED TV" or "LED screen" is an LCD panel lit from behind by LEDs: the diodes provide light, not the image.
The second is direct-view LED: a wall built from tiles of individual diodes, where the LEDs are the picture. This is what large outdoor displays and seamless indoor walls use. Its defining spec is pixel pitch, the millimetres between diodes, which sets the minimum viewing distance. A 10mm pitch is fine across a car park and unreadable close up; a 1.5mm pitch works in a lobby and costs many times more per square metre.
The caveat is brightness, and it runs the other way from what people expect. Direct-view LED is bright enough for direct sunlight, which makes it the only real option for outdoor, and far too bright indoors at full output, where it must be dimmed substantially or it is genuinely uncomfortable to stand near. Specify the indoor brightness you will actually run at, not the headline figure.