In UML, theisSubstitutableproperty of a generalization relationship indicates whether instances of the child classifier can be used wherever instances of the parent classifier are expected, that is, whether the subclass is substitutable for the superclass. When this property is set to false, it means that the child classifier cannot be substituted for the parent classifier. This property is part of the UML metamodel for generalization and affects how inheritance is interpreted in terms of substitutability, as described in the UML 2.x Superstructure Specification.