MultiBodies are internally grouped objects. This means that the MultiBody's objects are treated as a single node in the → “Nodes” and → “Relationship Editor”, but in the viewport you can see the individual objects. Typical examples are → fragmented objects or → object arrays:

You do not have access to these individual objects via a MultiBody's → "Node Params" panel – your changes will be applied to all included nodes.
The objects' basic properties are listed under File > Summary Info...
If you want to perform per-object changes right-click on the MultiBody under "Nodes" and choose → "Spreadsheet".

The "Detail" section of a MultiBody's "Spreadsheet" showing the properties of the individual nodes.

A MultiBody can be a → passive, active or rigid body or a soft body. In the latter two cases, the MultiBody's objects are able to interact with each other in the same way as separated objects. The only difference is that all of the MultiBody's objects share the same settings for → object friction, → elasticity, etc. The bodies' individual masses, on the other hand, are controlled via a common → density parameter:

density = mass / volume
and therefore mass = density * volume

It is possible to combine multiple external objects to a MultiBody during import:

Object Dynamics shelf > MultiBody. With this option you are able to choose which objects should belong to a MultiBody.
Object Dynamics shelf > MultiBodies from Folder. Here, the SD files inside a folder are translated into MultiBodies.

There are few more things you should know about MultiBodies:

You can import as many MultiBodies as required.
Individual MultiBodies can be removed from the scene without affecting already loaded SD nodes.
Imported MultiBodies do not support animation.
Imported MultiBodies are → unlocked by default and can be positioned, rotated, and scaled.
A MultiBody's individual → export resources are activated by default.

Browser not supported