There was recently a thread that dealt in part with this topic, but for the life of me I cannot find it. My question is: WHAT IS THE DEFINITION OF A TAP CONDUCTOR? I find it nowhere in the NEC. More specifically, when you terminate a #8 copper in a box for a raqnge recept, can you pigtail the grounds to a smaller AWG? Is this a "tap"?

You will find your definition in 240.2.

Also, what you describe is not a tap, it is an undersized equipment grounding conductor

Tripp, you're hunting for table 210.24....

Also study 240.5 particularly 240.5(2)

Also study 210.19 (A)(3) exceptions #1,#2

Also study 210.19 (A)(4) exception #1 (c)

These tap conductors are limited to 18 inches.