Resistor
Also called Resistors
A resistor is a circuit element made to have a known resistance, drawn as a zigzag on a schematic. It converts electrical energy into thermal energy, and on both AP exams it is assumed to be ohmic unless a question says otherwise.
Device against property. A resistor is the component; resistance is the number that component has, in ohms; resistivity is the property of the material it is made from. The AP Physics 2 CED flags that trio by name, warning that students must know the differences in meaning between current, potential difference, resistance, resistivity and capacitance.
What a resistor does with energy is stated at 11.4.A.1. Power is the rate at which energy is transferred, converted or dissipated:
The first is printed on both equation sheets; the second pair is labelled a derived equation in both CEDs. Statement 11.3.B.1.iii adds that resistors convert electrical energy to thermal energy, which may change the temperature of both the resistor and its environment.
Two idealizations you are given for free. Both AP equation sheets list among their exam conventions that resistors and lightbulbs are ohmic, so a resistor's does not drift as it heats. And ideal wires have negligible resistance (11.5.B.1), though the CED adds the caveat that wire resistance may only be neglected if the circuit contains other elements that do have resistance.
A resistor carries current in either direction with no preference, and it never uses current up: the current leaving equals the current entering. Combining several of them is the job of the series and parallel guide, and the linearity that makes it possible is ohmic behaviour.