Class A, Class B, and Class C amplifiers are three types of electronic amplifiers that differ in their operation and efficiency. Class A amplifiers conduct over the entire input signal cycle, providing high linearity and low distortion but are less efficient, typically around 20-30%. In contrast, Class B amplifiers conduct for half of the input signal cycle, improving efficiency to about 50-70% while introducing some distortion. Class C amplifiers conduct for less than half of the cycle, achieving even higher efficiency (up to 80%) but are mainly used in applications like radio frequency transmission due to their non-linear characteristics.