When you pick target objects, you designate each target as a Reference, Move (the object itself), Copy, or Instance, according to the radio button selection in the Pick Targets rollout for morph objects.
This choice specifies how the morph object uses the target object. Base your selection on how you want to use the scene geometry after you create the morph.
Copy: The morph object uses a copy of the target. The original target object is unchanged.
Use Copy when you want to reuse the target geometry for other purposes in the scene.
Move: The morph object uses the target object itself, moving it into the morph. The original target object disappears and is no longer available after the morph is created.
Use Move if you've created the target geometry to be only a morph target, and have no other use for it.
Instance: The morph object uses an instance of the target object. If you later change the original target object, the morph object changes as well; and if you change the morph target, the original object changes.
Use Instance to synchronize morphing with animated changes to the original target object.
Reference: The morph object uses a reference to the target object. If you later change the original target object, the morph object changes as well; but if you change the morph target, the original object does not change.
As previously mentioned, you can use an animated object or another morph as the target of a morph.