Family Sharing refers to an action on an Apple decide where you can share apps, iBooks, music, etc. with your family members if you pay for that option.
Family Sharing makes it easy for up to six people in your family to share each other's iTunes, iBooks, and App Store purchases without sharing accounts. Pay for family purchases with the same credit card and approve kids' spending right from a parent's device. https://www.apple.com/icloud/family-sharing/