For a visual guide on the hardware involved in these classic consoles, you can see how the interior components are structured in this breakdown:
The phrase in the context of Power Up [Indie] [Jtag/RGH] most likely refers to the recommended hardware components for a stable Xbox 360 mod, specifically solid-core Kynar wire .
: This is considered a "solid piece" of equipment because it is easy to maneuver, holds its shape when bent around components, and prevents accidental shorts that are common with stranded wire.