The electron is really fast and zips around the nucleus in a flash. It’s so quick that you can’t really tell exactly where it is at any one moment because it’s always moving. But if you sit there and watch it for a long time, say, for many zips around the nucleus, you’ll start to notice something interesting.
Even though you can’t pin down its exact location at any moment, you’ll see that it spends most of its time in a certain area around the nucleus. It’s like when you’re playing tag in a big field, you might run all over the place, but you tend to hang out more in some parts of the field than others. This favorite ‘hangout’ spot is what we call “time-averaged position” of the electron.