A factory reset brings the phone back to how it was when you first got it.Means your stuff, apps, and settings get erased.Phones like iPhone or Android devices. This process gets rid of all downloaded apps, photos, videos, contacts, messages, call logs, saved passwords, and customized preferences. It basically removes everything you added after setting up the phone. The phone's operating system stays. It goes back to its original settings. Any software updates you already have usually stay.