Wiktionary
vb. (present participle of downcast English)
Wikipedia
In class-based programming, downcasting or type refinement is the act of casting a reference of a base class to one of its derived classes.
In many programming languages, it is possible to check through type introspection to determine whether the type of the referenced object is indeed the one being cast to or a derived type of it, and thus issue an error if it is not the case.
In other words, when a variable of the base class ( parent class) has a value of the derived class ( child class), downcasting is possible.
Usage examples of "downcasting".
By the time they brought the sailboat in Alan Savage was enough at ease with Graice Courtney to say, jokingly, with his quick shyly aggressive smile and the habitual downcasting of his eyes that was seemingly a sort of tic with him, Too damn bad, my mother found you first.