Imagine you have a big lego city that you love. You have lots of cool buildings and streets built out of legos. One day, your parents decide that they want to add a new building to your lego city but they can't find the right spot to build it. So, they start knocking down some of your buildings to make space for the new one.
Brusselization is kinda like that, but with real cities instead of lego ones. In the 1950s and 60s, many European cities like Brussels were growing really fast and needed more space for new buildings. Instead of finding new empty land to build on, they started knocking down lots of old buildings and replacing them with bigger, more modern buildings.
But people didn't like this very much. They didn't want to see their beautiful old buildings destroyed to make way for big, ugly new ones. They also didn't like how the new buildings changed the feel and character of their neighborhoods. So, today, we use the word "Brusselization" to describe the practice of tearing down old buildings to make way for new, often disliked, ones.