I'd have to see the context. It could mean a continuing silence; more likely, it could mean a silence kept between two or more people, all of who are conscious that the silence is being deliberately kept up by all parties. I could be wrong, but that is my guess. If you can give me the context, as I said, I could probably do better.

This is a phrase used artistically, in a movie title, a book, or a poem. It is art. It means whatever a person takes from it.

Give us more information on the text you extracted that expression from, so we can help you out.

It should be obvious from the context.