Planar transistor
Beginner
The flat kind of transistor used for most of chip history. Its gate sits on top of the channel, like a lid.
Novice
A MOSFET whose channel is a thin layer at the flat top surface of the silicon, with the gate lying on top. Its width is drawn freely in the layout, but the gate only acts from one side.
Expert
Single-gate MOSFET on a bulk (or SOI) wafer. In bulk, the gated depth is set by doping, so short-channel control costs channel doping, mobility and random dopant fluctuation. Planar bulk led until Intel’s 22 nm FinFETs in 2011; planar FD-SOI is still made for low-power parts.
Explained in Fins and nanosheets (Transistors).
See also: Multigate transistor, FinFET.