Set State
Pickable
Makes the selected layers normal (pickable).
In the Object Lister, pickable objects are indicated by this icon: 
Reference
Sets the layers to be visible but not pickable. Use this setting to snap to objects without picking them.
In the Object Lister, pickable objects are indicated by this icon: 
Inactive
Sets the selected layers to be templated (inactive).
Like objects templated with Display > Template. The objects are visible but not snappable or pickable.
In the Object Lister, inactive objects are indicated by this icon: 