"Share Forward" is the ability share a property that has been shared with you. When someone shares a property with you, they decide whether you can re-share that property with others. When you first share a property that you own, you decide whether or not to grant Share Forward permission to the person you are sharing with.
When you grant “Share Forward” permission, the person you are sharing with cannot share with more permissions than they were given. For example, if you share a property as Read Only for every type of data (Property, meters, and certification) then the person can Share Forward, but can only grant Read Access, not Full Access, to this property.
For more information, see our 5-page guide: "How to Share Properties with Others."