A backup of a website is a copy of its content, that's kept on another web server and may be restored if something happens. This feature is very handy, because you cannot know if a script update shall not fail or if you will not eliminate something by mistake - a file, a folder, a database entry, and so on. If your Internet site is backed up, it may be restored the way it was before the problem appeared, so there won't be any damage, or at least it will be little, depending upon the particular scenario. Keeping backups on your computer isn't very feasible, because you'll have to do it at least once every day and you may still lose information in case your last backup is not recent enough. In this light, you'll have to rely on your web hosting company, so you have to double-check their policy on the backups, due to the fact that some providers create backups only once each week, which will do no good if something wrong happens with a site that is being used and updated all the time, such as an online store, for instance.