Though "invisible" is usually associated with things we see, aspects of music can also be invisible to our ears. Robert Adams explains how tonality can be invisible.
A similar situation can exist with tonality. Notice I said can exist, because it does not always. In much of the Western art music repertoire, tonality is clearly heard every time we hear the stabilizing effect of the tonic chord providing respite from harmonic tension, or bringing the music to a temporary or concluding rest. While all this is so, there is also the invisible yet ever present aspect of tonality. Whether or not we are hearing the tonic chord, we nevertheless are constantly aware of what the tonic is. We know this because we audiate the tonality of the music we are listening to regardless of what chord we may be hearing at any given moment. So when the tonic chord is not being heard, the tonality is still there, invisible yet present because of our audiation.
As tonality became less explicit in the late nineteenth century, composers became more and more reliant on the listener’s ability to retain the tonic in mind while physically hearing it less and less. The whole concept of chromaticism and impressionism relies on this very thing. If we were not able to audiate the tonic amid chords stretching further and further away from the tonic, the tension, angst, and beauty of those chords and their dissonances would not be possible. As long as a composer gives listeners enough indications of a tonality, they can hear a piece as tonal and be aroused by the scarcity of physically present affirmations of that tonality. To the extent that a composer does this, he or she has created invisible tonality; tonality that is heard through audiation but not explicitly in the music itself.
Composer Piotr Lachert has written music that has invisible tonality in abundance. If you listen to his music, you will find that you rarely hear a tonic chord, yet always seem to know what it would be if you were to hear it played. He gives you just enough indication of a tonality to enable you to audiate what he has left out–the tonic. I've provided a link to a performance of his "Three Preludes" for solo piano. I hope you enjoy them.