Dematerialization is when you execute a command to drop subscriptions at the replicate Replication Server.
The replicate Replication Server selects data from the replicate data server to construct the dematerialization queue. The replicate data server uses its sort order to select the rows.
The replicate Replication Server uses its sort order to throw out rows belonging to other subscriptions.
The replicate Replication Server deletes the remaining rows from the replicate database.