Edit and Object Modes
This will create a visually-identical copy of the selected object(s).
The copy is created at the same position as the original object and
you are automatically placed in Grab mode. See the examples below.
This copy is a new object, which shares some data-blocks with the original object
(by default, all the Materials, Textures, and F-Curves), but which has copied others,
like the mesh, for example. This is why this form of duplication is sometimes called “shallow link”,
because not all data-blocks are shared; some of them are “hard copied”!
You can choose which types of data-block will be linked or copied when duplicating:
in the User Preferences.
The Cube object was duplicated.
Cube was duplicated, using Shift-D.
Both these cubes has separate meshes with unique names:
The original left cube is being edited, the duplicated right cube remains unchanged.
The mesh data has been copied, not linked.
Likewise, if one cube is edited in Object Mode, the other cube remains unchanged.
The new object’s transform properties or data-block is a copy, not linked.
When the cube was duplicated, it inherited the material of the original cube.
The material properties were linked, not copied.
See above if you want separate copies of the data-blocks normally linked.
You also have the choice of creating a Linked Duplicate rather than a Duplicate;
this is called a deep link.
This will create a new object with all of its data linked to the original object.
If you modify one of the linked objects in Edit Mode,
all linked copies are modified. Transform properties (object data-blocks) still remain copies,
not links, so you still can rotate, scale, and move freely without affecting the other copies.
Reference Expl. Duplicate Example for the discussions below.
In the Duplicate Objects Operator panel the Linked checkbox is checked unlike with Duplicate.
If you want to make changes to an object in the new linked duplicate independently of the original object,
you will have to manually make the object a “single-user” copy by LMB
the number in the Object Data panel of the Properties editor. (See Data-Block Menu).
The Cube object was linked duplicated.
Cube was linked duplicated, using Alt-D.
Though both these cubes are separate objects with unique names:
the single mesh named
Cube, is shared by both.
As a mesh is edited in Edit Mode in one object, the same occurs in the other cube as well.
The mesh data are links, not copies.
In contrast, if one of these two cubes is rotated or rescaled in Object Mode, the other remains unchanged.
The transform properties are copied, not linked.
As in the previous example, the newly created cube has inherited the material of the original cube.
The material properties are linked, not copied.
A common table has a top and four legs. Model one leg,
and then make linked duplicates three times for each of the remaining legs.
If you later make a change to the mesh, all the legs will still match.
Linked duplicates also apply to a set of drinking glasses,
wheels on a car… anywhere there is repetition or symmetry.
Linked Library Duplication
Linked Libraries are also a form of duplication.
Any object or data-block in other blend-files can be reused in the current file.
If you want transform properties (i.e. object data-blocks) to be “linked”,
see the page on parenting.