Reification is a really big word that means turning something that isn't real into something that is treated like it is real. Imagine you have a toy car and you pretend like it is a real car that you can drive around. That is sort of like reification, because you are treating the toy car like it is something it is not.
In Marxism, reification is the idea that people start to think of things like money, property, and even people as if they are objects, like they don't have feelings or thoughts of their own. This can happen when things become so important in society that people stop thinking about what they actually mean and how they affect others.
For example, if someone owns a lot of property, they might start to think of it as theirs and only theirs, without thinking about who used to live on that land or who might need it more than they do. This is reification because they are treating the property like it is just an object that they own, instead of thinking about the people and history behind it.
In short, reification means treating things like they are something they are not and in Marxism, it is used to describe the way people can dehumanize others and treat them like objects instead of thinking about their feelings and needs.