From Sterwiki

Social mortgage is a term used in Catholic social teaching. According to this body of thought, the social mortgage is the conditions under which humanity is allowed to use the goods of the world, which are viewed as part of God's creation. Use of the world's resources is bound to responsibility towards the rest of humanity. Although there is a right to private property, it is not an absolute right.
In particular, no one has the right to accumulate large amounts of private property while others in the world lack the basic requirements for survival and development.