A backup is a copy of a website that is kept on a different web server and can be restored if something goes wrong with the live Internet site - a failed script update, an accidental deletion of some file or of the whole database, etc. Restoring the site the way it was shall take away or reduce the damage the problem may have caused, that's by all means a much better alternative than having to rebuild your whole website from scratch. Although you may download a copy of your content on your PC, keeping a backup is a feature that nearly all web hosting companies offer as part of their plans. You must check how often they do that, though, because some providers generate a backup just once every couple of days, which can be far from enough for a booking website or an e-commerce portal in which the data is updated each day. It's adviseable to see how quick and easy a backup can be restored, which could be crucial if some problem appears on your website.