What is "space sharing"?

Somewhat the opposite of time sharing. While in time sharing a resource is used for a while by one entity and then the same resource can be used by another resource, in space sharing the space is shared by multiple entities but in a way where it's not being transferred between them.

It's used by one entity, until this entity decides to get rid of it. Take for example storage. In storage, a file is yours, until you decide to delete it.