What is veiled symbolism?

In general usage, it is symbolism that is not entirely obvious, but overly subtle, either. Much like a veil hides a bit, but you can still see a bit through it.

"The Chronicles of Narnia" by C.S. Lewis is a good example of veiled symbolism. It's not so entirely obvious that Aslan is God that a person is offended, or jolted out of the story, but it's not overly subtle, either.