Reification is the “act of materializing”. In other words, to reify is “to convert into or regard as a concrete thing”. Another more specific definition describes it as “representing a human being as a physical thing deprived of personal qualities or individuality”.
Is it just me, or does this sound like a made-up word? I’m used to seeing the prefix re- in words like redo and rediscover. I’m used to seeing the suffix -fication in words like modification and verification. So when I see this strange word reification, I think it’s just a prefix and suffix together with no real word in between them! Thankfully, the Online Etymology Dictionary shows that the re- in this word is actually from the Latin stem of res, meaning “thing” in Latin. And here’s a little did-you-know tidbit: the German word for reification, a la Marxism, is Verdinglichung.
See Wikipedia’s page on reification for its specific meanings in computer science, linguistics, and yes, Marxism too!