First, there's no way you're gonna be able to know if we looked it up. Second, do you know? If so, why are you asking the question. If not, why ask it in that way? Third, techniques used to help give the feeling of how far away or close an object is to the "camera."
There is no real way to say it, but the best way to explain it would be to make the user believe that the signature has a far away part, and a close up part. Depth is the compilation of an FG, BG, Focal, and blurring. It's basically like an illusion to make the user believe it's 3D.
Not techniques. The first part of that paragraph is unnecessary. I just wanted to see how smart the GnA section is, because I was recently told my latest image had "Reverse Depth"
It's hard to explain, but.... Due to the one possibility of dimension, 2D- no 3D, depth helps the piece look as 3D as possible. With certain tools, tricks, or illusions, you can add depth to a piece. Without depth the piece would most likely be more boring and feel too 2Dimensional.
Why does it matter? Curiosity? Oops. Didn't notice the thread was 5 days old. Also, re-reading that post, I don't know what I was thinking. Really nothing about what depth is in it.