Brown Tabard

Brown Tabard was a rank in the Tarovian martial arts.
Nardole reached the rank of Brown Tabard. (TV: The Lie of the Land)
== Behind the scenes ==
This is likely a reference to the coloured belt ranking system used in some styles of real life martial arts. In such rankings, a brown belt is most often the second highest category, below a black belt. 
A tabard is a short, usually sleeveless, coat that is open to the sides and put on by lifting it over the head. 
Category:Ranks