This page defines a prefix.
Prefixes are used by this wiki to quickly alert the reader to the source of a statement. The most common of these is TV, which indicates the source is a televised story.
The prefix DCOM indicates the information cited comes from BBC DVD commentaries. It can be compared to PCOM, which indicates the podcast commentaries made available during the RTD era. The necessity for two separate prefixes results from there being two different, BBC-released commentaries for many BBC Wales episodes of Doctor Who.
Thus, DCOM: Last of the Time Lords indicates an entirely different recording than PCOM: Last of the Time Lords.