The ability to use symbolic representation or logic. The opposite of abstraction, according to Carl Jung, is concretism.
Example: A middle schooler is struggling with his algebra homework; he can’t seem to wrap his head around the concept of variables.
Grinnell, R. (2018). Abstract Thinking. Psych Central. Retrieved on April 24, 2018, from https://psychcentral.com/encyclopedia/abstract-thinking/