Heat capacity
Definition
Heat capacity tells you how stubborn a substance is about changing temperature — how much heat it takes to warm it by one degree.
Symbol: · Unit: J/K
Technical definition
C = Q/ΔT, in J/K. It scales with the amount of material; the per-kilogram version is specific heat capacity c, so C = mc for a uniform object.
Example
A 2 kg cast-iron skillet (c ≈ 460 J/(kg·K)) has a heat capacity of 920 J/K — it takes 920 joules to raise it by one degree, which is why it stays hot long after the stove is off.
Common confusion
Heat capacity and specific heat capacity are not the same. Heat capacity belongs to a particular object (a 2 kg skillet); specific heat belongs to the material (cast iron) and doesn't care how big the piece is.