The Instances package (9.10) targets the big OOP paradigm of object-class relationship. It allows to illustrate a 'snapshot' of an object during run-time. Note that this isn't modelling the M0 (run-time instances) layer of the 4 layer meta-model hierarchy, but at the M1 (User model)-layer as the class itself.
A slot represents a structural feature
The slot class owns the instance value (as valueSpecifications) of the structural feature
For a class, this would be the attributes/properties
The instanceSpecification is the 'Instance' of one or more classifiers
The InstanceSpecification owns slots for the structuralFeatures of it's classifier(s)
It can have a specification for it's own value
The instanceValue is the identifier of an instance (I'm not sure if this is correct)
Up to now all classes of the meta-modell are abstract (not instancible). Once there are concrete classes, I will see how an instance in uml will look like.