What does System Data mean in iPhone storage? System Data is one of many categories in your iPhone storage. It contains important system files and any data that doesn't fall neatly into the other categories. Clearing the System Data on your iPhone can be a real space saver when your iPhone storage is full and you need to clear up space for an iOS update or to install a new app. We'll cover what System Data means and how to clear System Data on the iPhone or iPad to free up space.