Stack

STACKING is the placement of objects one on top of another. PowerPoint stacks objects automatically as they are added to a slide. The first object drawn or inserted is on the bottom, and the last object drawn or inserted is on top. The placement of the objects can be changed by using the stacking commands on the 'Draw' menu: 'Bring to Front', 'Send to Back', 'Bring Forward', and 'Send Backward'.

BRING TO FRONT moves the selected object to the top of the stack.
SEND TO BACK moves the selected object to the bottom of the stack.
BRING FORWARD moves the selected object one location closer to the top.
SEND BACKWARD moves the selected object one location closer to the bottom.

To select an object in a stack, press TAB or SHIFT+TAB to move through all the objects until the desired object is selected.

NOTE: Overlapping objects in a stack can be one way to create special shapes and effects, such as a donut shape, or a crescent shape.