What is "polite" sound?

Thinking about the question, thank you, I associate "polite" with speed or the lack of it. That connects to three factors: PRaT, dynamics and HF extension. Ouch, what a dismal fate, to be lacking in all of these! The word "polite" is... polite, of course, and IME doesn't usually refer to really horrible sound, just sound that is more or less easy to ignore. Better than sound which grabs your ears and twists. Not polite.

Seems obvious that there would be degrees of politeness. Polite compared to what? I don't especially associate Classé with "polite" but then my definition of polite sound was formed by my Dad's old system, a pair of B&W DM14s being driven, if that's the right word, by a 45wpc Sherwood solid-state receiver.

Most likely would be some British speakers "driven" by a French amp.

Polite by me is interpreted as opposite of forward...a laid back presentation. I find Verity and Vandersteen fit this description.

"Polite" sound is often what reviewers say when they can't define a specific defining characteristic of a component or speaker (i.e. descriptors like deep bass or scintillating highs, edgy, bright, harsh, sibilant or recessed don't seem to apply etc.)

In a high quality system this is usually indicative of a good design especially when the reviewer just thinks the sound is very natural and convincing. It is another way of saying that nothing stands out like a sore thumb about the design and therefore the system is likely to translate well too most recordings and genres. (Unfortunately this type of system may not sell well in a shop demo, however, there is a higher probability that you will not tire quickly of a system that is polite)