Suggest changing section title "Building Indexes Concurrently" to "Building Indexes Using the CONCURRENTLY Parameter" to eliminate any ambiguity.
That seems worse. If anything the title should answer the question "Concurrent with What?". Right now one infers it means with other read/write activity on the table - as opposed to, say, additional indexing operations on different connections, which may or may not touch the same tables. This is the concept of concurrency we want to refer to here - the parameter has already been described above.
