A backup of a website is a copy of its content, that's kept on some other server and may be restored if something happens. This function is rather effective, since you can't know if a script update won't crash or if you will not delete something unintentionally - a file, a folder, a database entry, and so on. When your Internet site is backed up, it could be restored the way it was before the problem appeared, so there shall not be any damage, or at least it shall be very little, dependant upon the particular situation. Keeping backups on your computer system isn't very feasible, since you would have to do it at least once per day and you may still lose info in case your last backup isn't recent enough. In this light, you will have to rely on your website hosting provider, so you ought to double-check their policy on the backups, since some companies create backups only once each week, that will do no good if something goes wrong with an Internet site that is being used and updated constantly, such as an online store, for instance.