There are various steps to producing a DVD, but they can be split into two major parts: 1) authoring (creating the content and formatting a disc image), and 2) replication (cutting a master disc and stamping out hundreds or millions of copies).

[A] = authoring (including encoding, DVD-R creation, and premastering).
[R] = replication (mastering, check discs, and mass production).
[D] = duplication (short-run copying onto recordable discs)
Note that most replicators and duplicators have in-house authoring facilities or partnerships with authoring houses.