A backup is an exact copy of your files, your system files or any other system resources you need to protect. This precaution is necessary for all types of unpredictable events, like a system crash or when you remove or lose those files. The backup is supposed to be independent from your system and be used only when necessary. There are also cases when the system or those files become infected, and you need to recover them. Or when the system is blocked by a ransomware.