Dark silicon
Beginner
Parts of a chip that must stay switched off at any moment, because turning everything on at once would make it too hot.
Novice
The share of a chip that cannot run at full speed at the same time without breaking its power budget. It appears because the number of transistors per chip has grown faster than the energy each one uses has fallen.
Expert
Projected in 2011 at 21% of a fixed-size multicore chip at 22 nm and over 50% at 8 nm. The industry’s response has been specialization: accelerators that sit idle most of the time but do their one job very efficiently when used.
Explained in Specification (Design Flow).
See also: Dennard scaling, TDP (thermal design power).