Here's what Paul McGowan says about the question.
Continuing with Audiophile terms I find Transparency a much used term that perhaps is a bit nebulous and easy to overuse. One of the first things you notice about many of these terms is they are somewhat self descriptive; as any really good and valuable word should be.
Transparent means you can see through it and the opposite would be opaque; the middle would be translucent. The greater the transparency the more “see through” qualities one is getting in the music.
The first time the term really struck home with me was with my first pair of electrostatic loudspeakers, the Quads, followed by Acoustats and then Martin Logans. Yup, for a period in my life, I was all about electrostatic loudspeakers because they had a see-through like quality – an increase in transparency – like nothing I had heard before. The fact that you had to hold your head in a vice and they didn’t have bass or dynamics didn’t bother me till later, but that’s another story.
If you’ve ever had the opportunity to hear a really great pair of electrostats you’ll know what transparency means. One of the first tracks I remember hearing on an electrostat was from a Sheffield Direct To Disc recording of Lincoln Mayorga playing Stevie Wonder’s cover of “You are the sunshine of my life”. That was a memorable cut and, for the first time, I could actually see through the group playing. More than depth and separation of instruments, this transparency I am referring to was like lifting a veil that covered up the inner details of what I was hearing. I could hear into the music. And deeply.
Transparency is still a quality I look for in electronics.
Circuit elements I have found that detract from transparency are capacitors in the signal path and amplifying devices with too little current flow. I have also discovered power supplies have a major impact on the transparency as does a measured increase in IM (intermodulation Distortion).
I hope this explanation helps your ability to see the word a little clearer.