I once flippantly described the process of CD mastering as "taking the tapes which people think are finished, and finishing them". There is, of course, an element of truth to this but inevitably there is rather more to it than that.
A finished CD master must obviously sound, and run, exactly the way that the final album or single should sound. This involves basic stuff like
There may be other issues too, for example, making sure that the record company / printers are supplied with the correct titles and timings and that the final master meets the specification laid down by the replication plant. Ideally a printout of the BLER and the PQ timings should also be supplied to the replication plant.
Since I began CD mastering the preferred delivery format has changed a number of times. The Sony 1610/1630 format and Exabyte tapes are now a thing of the past. These days we usually supply DDP image files on CD-ROM or DVD-ROM. Online delivery by secure FTP (File Transfer Protocol) is also now commonplace.
We can now produce DDP v2 filesets (with optional CD-Text). ISRC codes can also be added to the final master if these are supplied ahead of time. We can also master for iTunes.