When people with money start fixing up poor neighborhoods, that’s gentrification. Sounds great, except it usually means the poor residents can’t afford to live there anymore and have to move.
In the United Kingdom, the gentry are the highest class of people aside from royalty. When you add -fication (the suffix that means “making”), you see how gentrification means "making something suitable for a higher class of people," usually the middle class (the upper class already have their mansions). When a neighborhood goes through gentrification, buildings get makeovers, new businesses open, and many people who’ve lived there their entire lives must leave because everything gets more expensive.