Bumpmaps are items that add 'depth' to textures from what I have heard. They involve making the texture on top of it (the Bumpmap items are 'layered' under earth a regular texture item) seem to have more of an indented look and feel to it by using shadows.
Whether or not bumpmaps still function correctly is another story. I would not invest in bumpmaps just yet. (There is debate about them working and not working currently)