In web design, what does it mean to have everything in "one layer"?

Question

I'm creating artwork for a website company, and I'm asked to give them my files so that all the work is in one layer.

Answer 1

For the artwork, I imagine they want all layers flatten which means saving the images in a normal web image format and not a format like *.psd (Photoshop). This keeps them from having the exact same graphics editor you used to open them up.

( http://en.wikipedia.org/wiki/Layers_(dig... )

Ron