The duster coat was a form of coat, sometimes with a cape, to protect from dust.
Jackson Lake wore a dark tan duster coat when he and Rosita Farisi showed the Tenth Doctor his 'TARDIS' balloon during the 1851 Incident. (TV: The Next Doctor)
The Eighth Doctor wore a black leather duster coat when helping General George Armstron Custer and Tatanka Yotanka ato stop Count Jodafra's Windigo in America during 1875. (COMIC: Bad Blood)
While searching for the Eighth Doctor as part of his Regeneration Operation, the Bruce Master wore a duster coat of black leather. (TV: Doctor Who)