The IHS is the metal cover of the processor. The IHS acts like a heat sink, dissipating heat from the CPU to the cooler. It also protects the processor from the inside out. Also, this is the open part of the processor after installation and the surface to which the thermal paste is applied.
CPU Cooler: The CPU cooler controls the temperature of the CPU. Typically, air or liquid keeps the CPU at an optimal temperature while the system performs complex tasks.