Markov was a location on a class M planet over which Makull's species presided.

Markov was the location of a polaric accident, prompting more support for groups of people who protest against the use of polaric energy as a power source. (VOY: "Time and Again")

This location was only mentioned in dialogue.
In ultimately unused dialogue from the final draft script of "Time and Again", a cousin of Pe'Nar Makull, who was now dying of polaric contamination, had worked at Markov.