Minimization of electrical noise?
Your textbook is probably talking about decoupling capacitors. It looks like this:



(from http://www.learnemc.com/tutorials/Decoupling/decoupling01.html)

A small capacitor (most of the time 100nF) placed near the MCU from VCC to VSS. It filters away all the high frequencies, so that no noise gets to the MCU.

Why not a large capacitor? Basically because it doesn't respond that good on higher frequencies: What&#39;s the use of a decoupling capacitor near a reservoir capacitor?

A circuit:



(from http://ez.analog.com/docs/DOC-1420)

The red capacitors are decoupling capacitors. As you can see, two different values are used. This is to eliminate as much frequencies as possible. 

The blue capacitors are DC-blocking (AC-coupling) capacitors and are used to shift the center of the AC (RF) signal back to ground to match the dynamic-range of the receiving system. They are sized to minimize attenuation of the desired signal by presenting as low an impedance as possible at the signal's frequency band.