Okay, imagine you're playing with toys with all your friends at your house. But suddenly, so many people come over that your house can't handle all the toys and people anymore! That's kind of what happens with buildings and neighborhoods sometimes - they can't handle too many people living and working there without everything getting too crowded and messy.
So, to make sure things don't get too cramped, cities and towns sometimes make rules called "adequate public facilities ordinances" (APFOs for short). An APFO says that before a new building can be built or more people can move into an area, the city has to make sure that the "public facilities" (like roads and schools) can handle all the extra people. It's like making sure you have enough toys for everyone to play with before inviting more guests to your toy room.
Cities and towns might use different ways to check if their public facilities can handle more people. For example, they might count how many people are already living and working in an area, how many schools are already there, and how many roads there are to get in and out of the neighborhood. Then they'll figure out how many more people or buildings can fit without making things too crowded.
It might sound like a lot of boring grown-up stuff to worry about, but it's important because if too many people try to use the same roads, schools, and other public facilities, it can be unsafe or make it hard for everyone to enjoy living there. And that's no fun for anyone!