Needs some clarifications in Data Blocks section

[dSalieri]

Reading a chapter on Data Blocks, some questions arose. They are more tied to one specific sentence that causes misunderstanding.

A Shared Data Block has an identity (for the purposes of equality testing Shared Data Block values) that is address-free : it is tied not to the virtual addresses the block is mapped to in any process, but to the set of locations in memory that the block represents.

1. What does address-free mean? ("no address" or "free addressing"). I could not find such a term either in dictionaries or on the Internet.
2. This sentence explains what address-free means, but then there would be no question if the explanation were simple, but it is not simple. It says that the Shared Data Block is not tied to virtual addresses, but it appears as set of locations in memory. What is the difference between virtual addresses and set of locations in memory?