Ohm (Ω)

Take the potential difference across an object, divide by the current through it, and the answer is in ohms:

The AP sheets print this as $I = \Delta V/R$, the same relation solved for current.

The definition says nothing about the material. That is where the ohm parts company with resistivity. Resistance belongs to one particular object, and the sheet supplies the geometry separately as $R = \rho\ell/A$, so the ohms depend on what it is made of, how long it is and how thick it is. Two wires of the same metal have different resistances.

Ohmic is a convention, not part of the definition. Both electricity tables of information carry an exam-convention line saying resistors and lightbulbs are ohmic, meaning $R$ holds constant as the current changes, so a graph of $I$ against $\Delta V$ is a straight line through the origin with slope $1/R$. Real filaments are not ohmic: they heat and their resistance climbs. The ratio $\Delta V/I$ still has a value in ohms at every point of such a curve, it is simply not the same value everywhere.

The symbol is a capital omega, the only Greek letter appearing in any of the four AP unit-symbol tables. Spelled out in prose it is an ohm, lowercase.

Ohm is printed on the AP Physics 2 and AP Physics C: Electricity and Magnetism tables. An ohm times a farad is a second, which is the unit check behind $\tau = R_{\text{eq}}C_{\text{eq}}$.