Backup data is a copy of files, programs, or disks that can be used if the original is lost, damaged, or destroyed. Backing up data protects against accidental loss, corruption, hardware failure, and natural disasters. The document describes how to set up backup in Windows 10 by selecting a backup drive or network location and choosing which folders to back up. It also lists 5 ways to back up data, including using cloud storage services, external hard drives, CDs/DVDs, USB flash drives, and NAS devices.