A backup is a copy of a site which is kept on another hosting server and can be restored if something goes wrong with the live site - a failed script update, an accidental deletion of some file or of the entire database, and so on. Restoring the site the way it was shall remove or decrease the damage the problem may have caused, that's by all means a better option than having to rebuild the whole website from scratch. Though you can download a copy of your content on your laptop or computer, keeping a backup is a functionality that nearly all website hosting providers include as part of their packages. You'll have to check how frequently they do that, though, because some providers create a backup only once every week, which may be far from enough for a booking website or an e-commerce portal in which the information is updated every single day. It's also advisable to see how quick and simple a backup can be restored, which can be crucial if some problem appears on your website.