Conduction
Also called Thermal conduction
Conduction is the transfer of energy through a material by collisions between neighboring atoms, with no bulk movement of the material itself. It requires matter, so it cannot cross a vacuum.
One of the three thermal processes named in essential knowledge 9.3.A.2, alongside convection and radiation.
The defining feature is that the material stays where it is. Energy passes atom to atom while the atoms keep their places, which is the microscopic picture 9.3.A.3.i describes: in collisions between atoms from different systems, energy is most likely to be transferred from higher-energy atoms to lower-energy atoms. Convection is the contrast, because there the atoms travel with the energy.
Conduction needs matter, so it cannot cross a vacuum, and it is the pathway that always exists between two objects in physical contact.
It is also the only one of the three with a rate equation on the AP Physics 2 sheet:
The CED files that equation under 9.5.B.1 rather than under 9.3, so Topic 9.5 owns the calculation while Topic 9.3 owns the definition.
That rate answers a question the CED prints in the Unit 9 opener: why a tile floor feels colder than a bath mat in the same room. Their temperatures match. Tile has the far larger thermal conductivity, so it draws energy from a bare foot much faster. "Feels cold" is skin reporting a rate of energy loss, not a temperature.