Channel (inversion layer)
Beginner
The thin layer of electrons that a transistor’s gate pulls together under itself. It is the bridge that lets electricity cross the switch.
Novice
A thin layer at the silicon surface under the gate where the gate’s field has gathered so many carriers of the opposite type to the body that the surface behaves like the source and drain: n-type in an NMOS, p-type in a PMOS.
Expert
Forms in strong inversion once passes . Its charge per area is about , which is what the square-law model integrates. Why the surface inverts is covered in the optional physics chapter.