Slice Tool (k)
Slices you create using the slice tool are called user slices, Slices you create from a layer are called layer-based slices. (or) The slice tool allows you to create multiple images from one image or a layered Photoshop file. You can slice up the image using areas that you create using the slice tool or by using guides that you have applied. This allows you to save out images in preparation for the web very quickly.
You can move and resize user slices in Photoshop but not in the Photoshop Save for Web dialog box. You can also move and resize alices using numeric coordinates.