Questions about Unity Standard shader code

I'm trying to understand shaders and have some questions.
Here is the the Unity standard specular shader:

Code (csharp):

1.  
2. Shader "Standard (Specular setup)"
3.   SubShader
4.     {
5.         Tags { "RenderType"="Opaque" "PerformanceChecks"="False" }
6.         LOD 300
7.  
8.         // ------------------------------------------------------------------
9.         //  Base forward pass (directional light, emission, lightmaps, ...)
10.         Pass
11.         {
12.             Name "FORWARD"
13.         }
14.         // ------------------------------------------------------------------
15.         //  Additive forward pass (one light per pass)
16.         Pass
17.         {
18.             Name "FORWARD_DELTA"
19.         }
20.         // ------------------------------------------------------------------
21.         //  Shadow rendering pass
22.         Pass
23.         {
24.             Name "ShadowCaster"
25.         }
26.          // ------------------------------------------------------------------
27.         //  Deferred pass
28.         Pass
29.         {
30.             Name "DEFERRED"
31.         }
32.  
33.         // ------------------------------------------------------------------
34.         // Extracts information for lightmapping, GI (emission, albedo, ...)
35.         // This pass it not used during regular rendering.
36.         Pass
37.         {
38.             Name "META"
39.         }
40. }//end subshader
41.  

In the "META" pass, the code comment says "This pass it not used during regular rendering.".
What is considered "regular" rendering? Isn't this code automatically executed? If it isn't, what prevents the META pass from being executed?

 

Technically the names don’t do anything for rendering, they’re there for convenience of code readability, and for UsePass. What maters is each pass’s LightMode tag.

https://docs.unity3d.com/Manual/SL-PassTags.html

Each of those named passes has a different LightMode, specifically ForwardBase, ForwardAdd, ShadowCaster, Deferred, and Meta, in that order. The page above describes what each LightMode type is used for. Curiously Meta is not listed on the above page, but is instead documented here:
https://docs.unity3d.com/Manual/MetaPass.html

Basically the Meta Pass is not used by the main rendering pipeline, and is generally only used when baking lightmap data in the editor. It’s possible it might get used at runtime for some uncommon situations for Enlighten’s realtime precomputed GI, I don’t know for sure, but certainly not for the average use cases.

 

Thanks. Now I understand.