What is a backup?
A backup is an extra copy of the files on your computer or mobile device. It is typically stored in a separate location from the original files, such as on another drive or in the cloud. If anything happens to your files — if they go missing or get destroyed — then you will be very thankful you have a backup!
How does a backup work?
Note that a backup is an exact copy of whatever files and folder exist on the original. If a file is added to a backed up folder, then that file will appear in the backup. If that file is deleted, then it will be removed from the backup as well (although some backup programs allow recovery up to a certain period of time). This is the key distinguisher between backup and storage, wherein storage is a way to save files that may not exist in any other location (Dropbox and Google Drive are examples of storage).
Note that most backup software simply copies user files to another location–often an external hard drive or the cloud. User files include documents, photos, movies, downloads, and music. They do not back up the operating system, settings, or programs. For that, a “full system” or “bare bones” backup is required. Full system backups can be either clones or images, and they are most useful in the event of hard disk failure.