Explain what is a clean power amplifier?

@trevanian my amps are clean i wipe them with isopropyl alcohol once a week

@isochronism .
A very good quote.😄
B

Clean power could mean class D as well. Used the least juice and best on the power grid. 

There is clean. 
And then there is the cleaner. 
https://www.youtube.com/watch?v=yADf9QislaE

What is a clean "sounding" amplifier? My Macs, My Nords, and My Carys, My VTL use to be... SUPER clean, Krell, less clean Pass.

Dirty, there are to many good ones to pick a bad one, any more. Just a little looking will get you a good amp..

What is a clean "looking" amplifier, My Macs, My Nords, My Carys. All are covered, with a silk tablecloth, when not in use, once a month dusting. Chrome and shiny paint get waxed twice a year. Valves are pulled and glass polished, pins soft brushed, and cotton wad plunge, twice a year, also.

Clean is Clean