It means different things to different people, but what I mean by it is building cities and designing transit in a way that provides opportunities for people of different income levels, careers, and capabilities. If you're a WFH mom you should also be able to walk your kids to school. If you're a painter you should be able to hop on a tram or ride your bike over to your studio. If you're a white-collar software engineer and you make a ton of money, you probably have a larger house but you live in the same neighborhood and you go the same coffee shop as someone who works at a warehouse or helps take care of older people.

One of the contributing factors to racism and bigotry in America at least that we have stratified society and locked everyone into homes out in the suburbs where they don't interact with people from other socioeconomic classes, different ideas, or different life stages. It's easy to hate people when you read about them on the Internet. It's nearly impossible to do so when you see them at the park with their children living the American dream just like you.

Others may have different interpretations and such, but that's what it means to me in an over-simplified nut shell.