Power amplifiers come in classes determined by their design. Their classifications are listed by simple letters of the alphabet, but underlying that simplicity is a whole lot of complexity.
For example, amp classes as determined by their bias and turn-on cycle include A, AB, B, and C. The differences in this class of amps is determined by how much constant power they consume and when their output stage turns on and off.
Class H amplifiers are different. Their amp circuitry is rather common but their power supplies are variable: only a little voltage for small audio signals and jumping to big voltage outputs as the music gets louder.
And Class D amps are entirely different in the way they work altogether. These, of course, are Pulse Width Modulated amplifiers that work in fundamentally different ways than an analog amplifier.
Because of the similarity in nomenclature of amp classes (using the alphabet for classifications) it’s easy to think that amp classes are related to each other.
But that wouldn’t be accurate.
A, B, C, D, and F may be simple letters but the science behind them is a lot more complex.