Opposite of verb "abstract" and noun "abstraction"

American Heritage has concretize, but specify came to my mind.

concretize To make real or specific.

specify To state explicitly or in detail.

You may also consider TO REIFY and REIFICATION. Broadly speaking it means "to make real". (See http://www.thefreedictionary.com/reify).

Reification has a specific meaning in computer science as "the process by which an abstract idea about a computer program is turned into an explicit data model or other object" (quoting Wikipedia). You may wish to read the Wikipedia article.

Strictly in the Computer Science realm, we use "concrete" as the opposite of "abstract" as adjectives. You cannot instantiate (make one of) an abstract class; you can instantiate a concrete class. So "instantiation" probably comes close to the noun, and "instantiate" comes close to the verb. Purely in terms of taxonomy, you could use "generalization/generalize" when going up a class heirarchy towards the more abstract ("vehicle" is a generalization of "car") and "specialization/specialize" going the other way.