Instantiation is when you give a specific example to clarify an idea or opinion. The perfect instantiation of your uncle's love of dogs is the fact that seven Great Danes live in his house with him.
Instantiation, most simply understood to mean "exemplification," or "the ideal example or representation," is also a more complicated philosophical idea. The "instantiation principle" is essentially the concept that a characteristic or property can't exist unless you can point to a real-world instance of it. And in computing, instantiation is the act of creating a named object in a particular programming language. In everyday use, you might say your lovely new shirt is the instantiation of your sister's sewing ability.