A backup is a copy of a site that's kept on another hosting server and can be restored if a problem occurs with the live Internet site - a defeated script update, an accidental deletion of a file or of the whole database, and so on. Restoring the site the way it was will remove or reduce the damage the problem may have caused, which is by all means a certainly better alternative than having to rebuild your whole Internet site from scratch. Though you could download a copy of your content on your PC, keeping a backup is a function that most hosting providers incorporate as part of their packages. You'll have to check how frequently they do that, though, because some service providers create a backup just once every week, which might be far from enough for a booking site or an e-commerce portal in which the information is updated every single day. Make sure that you see how easily a backup may be restored, which can be critical if some problem appears on your website.