Critical listening is what reviewers do when a component is being evaluated. It involves knowing specific reference recordings, but it also requires some familiarity with acoustic instruments (for reviewers). A reviewer has to know how close to the ’real thing’ a component comes. And it is usually acoustic because the harmonics of such instruments are assumed to be known to most people. And that’s the problem.
A very large cross-section of people - nowadays - listen to mostly electronic music and otherwise "processed" music, something with no analogue in real life. Additionally, it seems that the last two (American) generations of students have had to take very little training in music (classes/band practice, you name it), and consequently, when people get into audio with no knowledge of how instruments sound, it is hard for them to do any ’critical listening.’ What are they basing their assessment on? A Hammond B-52?? One could base an assessment on that, but only if other instruments are also involved so that one can arrive at the best conclusion as to the traits of the component under review.
And while it doesn’t have to be acoustic, people are more familiar with say, a guitar than they are a synthesizer of whatever other electronic instruments there are.
So, critical listening is how you determine the traits of a component. Does it only play loud, or can it play soft, softer and softest and conversely loud, louder, loudest? Do you notice whether or not it is tonally right or is it ’off’ a bit? Does it have dynamics only in the upper midrange, or does it have dynamic expansion in all the other frequencies as well?
That is what critical listening is.