What are coupling and decoupling capacitors?
They are no different from normal capacitors. The Decoupling and Coupling refers to how the capacitors are used, not what they are made of or anything.

A decoupling capacitor is used as a mini battery or energy reserve. By placing it near an IC's power pins, it helps keep the power line steady, avoiding the minor fluctuations and ripple that exist in power circuits:


  A decoupling capacitor is a capacitor used to decouple one part of an electrical network (circuit) from another. Noise caused by other circuit elements is shunted through the capacitor, reducing the effect it has on the rest of the circuit. An alternative name is bypass capacitor as it is used to bypass the power supply or other high impedance component of a circuit.


Decoupling capacitors are typically in parallel with an IC or circuit.

Coupling capacitors on the other hand:


  In analog circuits, a coupling capacitor is used to connect two circuits such that only the AC signal from the first circuit can pass through to the next while DC is blocked. This technique helps to isolate the DC bias settings of the two coupled circuits. Capacitive coupling is also known as AC coupling and the capacitor used for the purpose is also known as a DC-blocking capacitor.


Coupling capacitors are typically in series with the signal.

Both types are typically common non-polarity-specific ceramic capacitors.