They're referring to logical replication, which is a relatively new feature.
The original mode of replication merely ships the WAL, which describes binary changes to data files. Every change comes in the form "set page 32435 in <file> to <bytes>", with no distinction between the operations that the changes represent.
Logical replication describes the changes logically. A change may be "insert <column values> into <table>" or "add <column name> of <type> to <table>". Since this format isn't tied to the underlying database file format, it offers greater compatibility between PostgreSQL versions. It also allows other applications to process the log and do things like listen for data changes and ingest them into other databases, queues, etc.
The original mode of replication merely ships the WAL, which describes binary changes to data files. Every change comes in the form "set page 32435 in <file> to <bytes>", with no distinction between the operations that the changes represent.
Logical replication describes the changes logically. A change may be "insert <column values> into <table>" or "add <column name> of <type> to <table>". Since this format isn't tied to the underlying database file format, it offers greater compatibility between PostgreSQL versions. It also allows other applications to process the log and do things like listen for data changes and ingest them into other databases, queues, etc.