Heat Sink is a passive (does not consume power) heat exchanger that transfers the heat generated from the device and dissipates it away. Above Image shows a parallel plate-fin extruded heat sink. When the heat sink is used without a forced fluid over it , it is known as passive cooling, as it generally relies only on natural convection and radiation to dissipate heat.
Heat Sinks come in a variety of shapes, sizes and materials.
Extrusion is still the most widely used manufacturing process for finned heat sinks.