Solid-State Amplifiers: What is distortion and how do I reduce it?

Based on a couple posts I made in several different threads, it occurred to me (after a suggestion from Moleculo) that this site could use a thread dedicated to solid-state amplifiers and how to keep their output clean. Maintaining clean output from a station is a foremost obligation of any radio operator and service, regardless of what class of license the op holds or if there is a license required at all.

I don't want to get into too much technical detail here, primarily because it's...

Solid-State Amplifiers: What is distortion and how do I reduce it?