A backup of an Internet site is a copy of its content, which is kept on a different web server and could be restored if something happens. This feature is very handy, because you can never know if a script update will not go wrong or if you won't erase something unintentionally - a file, a folder, a database entry, and so on. If your website is backed up, it could be restored the way it was before the issue appeared, so there shall not be any damage, or at least it'll be minimal, based on the particular scenario. Keeping backups on your computer is not very feasible, because you would have to do it at least once daily and you could still lose information if your last backup is not recent enough. In this light, you will need to rely on your website hosting company, so you must double-check their policy on the backups, as some companies create backups only once each week, which will do no good if a problem occurs with a site which is being used and updated constantly, such as an online store, for example.