What does it mean by USR led which is always turned off [HAP AC²]

RouterOS Beginner Basics
1

Hi there,
I’m curious to know, What’s the function of this LED. What does it mean. It is always turned off.
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Thanks.

2

It can be configured to report a variety of status information or be controlled by a script https://wiki.mikrotik.com/wiki/Manual:System/LEDS